94420 + Interview Questions in Chemistry in Class 12

1.	Radioactivity is a first-order process. Radioactive carbon in wood sample decays with a half-life of 5770 years. What is the rate constant (in "year"^(-1)) for the decay ? What fraction would remain after 11540 years?
Answer» Solution :We have `LAMDA= (0.6932)/(t_((1)/(2)))` `=(0.6932)/(5770)=1.2 xx 10^(-4)` per year Further, as the duration of 11540 years is just the DOUBLE of `t_((1)/(2))` (i.e., 5770 years) we can FIND out the fraction remained after 11540 years without using equation (24) as follows: After 5770 years, half of the SUBSTANCE would remain and after another 5770 years (i.e., a total of 11540 years) half of the half would remain, i.e., one fourth would remain after 11540 years.

Discussion

2.	Radioactive substance of 1 curie is the amount that can produce …………………………… disintegrations per second.
Answer» ANSWER :`3.7xx10^(10)`

Discussion

3.	Radioactive substances emit gamma-rays, which are
Answer» `+ve` charged PARTICLE `-ve` charged particle Massive particle Packet of ENERGY Solution :`GAMMA`-RAYS are neutral energy packet

Discussion

4.	Radioactivity is due to
Answer» Stable ELECTRONIC configuration UNSTABLE electronic configuration Stable nucleus Unstable nucleus Solution :Radioactivity is CHARACTERISTIC propertic property of unstable nucleus

Discussion

5.	Radioactive strontium as a result of radioactive fall out, is
Answer» `Sr^85` `Sr^90` `Sr^80` `Sr^95` ANSWER :B

Discussion

6.	Radioactive lead ._(82)Pb^(201) has a half-life of 8 hours. Starting from one milligram of this isotope, how much will remain after 24 hours
Answer» 1/2 MG 1/3 mg 1/8 mg 1/4 mg Solution :`n = (24)/(8) = 3, N = (N_(0))/(2^(n)) = (1)/(2^(3)) = (1)/(8) mg`

Discussion

7.	Radioactive isotopes that have an excessive neutron/proton ratio generally exhibit
Answer» `E^(-)` emission `._(2)He^(4)` emission `e^(+)` emission K-electron capture Solution :The isotopes having an EXCESSIVE n/p ratio EXHIBIT `e^(-)` emission

Discussion

8.	Radioactive elements were incorporated into the earth when the solar system formed All rocks and minerals contain tiny amount of these radioactive elements which breakdown spontaneously into more stable atoms overtime A commonly used radiometric dating technique relies on the breakdown of ._(19)K^(40) to ._(18)Ar ^(40) precise measurements of the amount of K^(40) relative to Ar^(40) in an igneous rock can tell the age of rock Choose the correct statements(s)
Answer» Rate of DISINTEGRATION of UNSTABLE nuclei increases with increase in number of nuclei and temperature Isotopes are formed DUE to `._(-1)beta^(o)` - decay Isotopes having even number of protons and neutrons must be stable nuclei Isodiaphers are PRODUCED due to `alpha`-emission Answer :D

Discussion

9.	Radioactive idoine is being used to diagnose the disease of
Answer» Bones Kidneys Blood cancer Thyroid Solution :`I^(131)` is used for GOITRE THERAPY, i.e., idoine deficiency

Discussion

10.	Radioactive elements were incorporated into the earth when the solar system formed All rocks and minerals contain tiny amount of these radioactive elements which breakdown spontaneously into more stable atoms overtime A commonly used radiometric dating technique relies on the breakdown of ._(19)K^(40) to ._(18)Ar ^(40) precise measurements of the amount of K^(40) relative to Ar^(40) in an igneous rock can tell the age of rock An igneous rock sample was found to contain 0.2 gm potassium and 0.6 gm of Ar The age of the igneous rock is (lambda of K^(40)=6.93xx10^(-10)year^(-1))
Answer» `1.2XX10^(8)` years `2xx10^(9)` years `2xx10^(10)` years `2.4xx10^(9)` years Answer :B

Discussion

11.	Radioactive elements can be categorised into (a) Neutron rich nuclide (b) Neutron poor nuclide In order to achieve stable n/p ratio these nuclide either emits beta^(-),beta^(+) (positron) or alpha-particle depending upon the n/p ratio of unstable nuclei and stable nuclei ._(53)P^(135) rarr Q+a Q rarr R+b [Note : only stable isotope of element P and Q are ._(53)P^(135) and ._(54)Q^(137) respectively] Element P,Q,R do not show any resemblence to currently known element ._(53)P^(135) rarr Q+a,t_(1//2)=1000 hrs Q rarr R+b,t_(1//2)=10 min Number of nuclei of Q and R respectively after 1000 hr if we start with 2 mol P [N_(A)=6xx10^(23)]
Answer» `6XX10^(23),6xx10^(23)` `6xx10^(22),6xx10^(23)` `2XX10^(20),6xx10^(23)` `10^(20),6xx10^(23)` Answer :D

Discussion

12.	Radioactive elements can be categorised into (a) Neutron rich nuclide (b) Neutron poor nuclide In order to achieve stable n/p ratio these nuclide either emits beta^(-),beta^(+) (positron) or alpha-particle depending upon the n/p ratio of unstable nuclei and stable nuclei ._(53)P^(135) rarr Q+a Q rarr R+b [Note : only stable isotope of element P and Q are ._(53)P^(135) and ._(54)Q^(137) respectively] Element P,Q,R do not show any resemblence to currently known element Particles a and b can be respectively
Answer» `._(2)He^(4),-1^(E^(o))` `.-1^(e^(o)),._(2)He^(4)` `.-1^(e^(o)),._(+)e^(o)` `._(2)He^(4),._(2)He^(4)` ANSWER :B::C

Discussion

13.	Radioactive disintegration isa first order reaction and it's rate depends only upon the nature of nucleus and does not depend upon external factors like temperature and pressure . The rate of radioactive disintegration (Activity) is represented as - (dN)/(dt) = lambda N , Where lambda = decay constant , N number of nuclei at time t, N_(0) = initial no. of nuclei. The above equation after integration can be represented as lambda = (2.303)/(t) "log" ((N_(0))/(N)) Calculate the half-life period of a radioactive element which remains only 1/16 of it's original amount in 4740 years :
Answer» 1185 YEARS 2370 years 52.5 years none of these SOLUTION :`N_(0) to (N_(0))/(2) to (N_(0))/(4) to (N_(0))/(8) to (N_(0))/(16) , t = 4740 = 4 xx t_(1//2) , t_(1//2) = (4740)/(4) = 1185`

Discussion

14.	Radioactive disintegration isa first order reaction and it's rate depends only upon the nature of nucleus and does not depend upon external factors like temperature and pressure . The rate of radioactive disintegration (Activity) is represented as - (dN)/(dt) = lambda N , Where lambda = decay constant , N number of nuclei at time t, N_(0) = initial no. of nuclei. The above equation after integration can be represented as lambda = (2.303)/(t) "log" ((N_(0))/(N)) What is the activity in Ci (curie) of 1.0 mole of Plutonium - 239 ? (t_(1//2) = 24,000 years)
Answer» 1.49 Ci 14.9 Ci `5.513 xx 10^(11) Ci ` NONE of these Solution :`A = lambda N , ((0.693)/(24000 xx 365 xx 24 xx 60 xx 60)) xx ((6 xx 10^(23))/(3.7 xx 10^(20))) cm^(-2)` `= 1484.79 xx 10^(13-15) = 1484. 79 xx 10^(-2) = 14.85 C `

Discussion

15.	Radioactive disintegration isa first order reaction and it's rate depends only upon the nature of nucleus and does not depend upon external factors like temperature and pressure . The rate of radioactive disintegration (Activity) is represented as - (dN)/(dt) = lambda N , Where lambda = decay constant , N number of nuclei at time t, N_(0) = initial no. of nuclei. The above equation after integration can be represented as lambda = (2.303)/(t) "log" ((N_(0))/(N)) Half-life period of U^(232) is 2.5 xx 10^(5) years . In how much time will the amount of U^(237) remaining be only 25% of the original amount ?
Answer» `2. 5 xx 10^(5)` years `1.25 xx 10^(5)` years `5 xx 10^(5)` years `10^(6)` years SOLUTION :`t_(1//2) = 2.5 xx 10^(5)` years , `N_(0) OVERSET(t_(1//2)) (to) (N_0)/(2) overset(t_(1//2))(to) (N_(0))/(4) , t = 2 xx t_(1//2) = 5 xx 10^(5)`

Discussion

16.	Radioactive distintegration is an example of
Answer» ZERO ORDER reaction first order reaction second order reaction third order reaction Answer :B

Discussion

17.	Radioactive decay is a statisticle process i.e., we cannot precisely predict the timing of a particular radioactivity of a particular nucleus . The nucleus can disintegrate immediately or it may take infinite time . Simply the probability of the number of nuclei being disintegrated at any instant can be predicted . the rate at which a particular decay process in a radioactive sample is directly proportional to the number of radioactive nuclei present and thus obeys first order kinetics . the factor dN/N expresses the fraction of nuclei decayed in time dt.t_(1//2) is the time in which half of the atoms are decayed and average life is the time for the nucleus to survive before decay .Which of the following relation is correct ? (t_(1//2) and t_(3//4) are time required to complete half and 3/4 decay respectively )
Answer» `t_(1//2)= 2 XX t_(3//4)` `t_(1//2) = 3 xx t_(3//4)` `t_(3//4) = 2 xx t_(1//2)` `t_(3//4) = 3 xx t_(1//2)` SOLUTION :

Discussion

18.	Radioactive disintegration differs from a chemical change in beings
Answer» An EXOTHERMIC CHANGE A spontaneous process A nuclear process A UNIMOLECULAR first ORDER reaction Solution :CHEMICAL change is extra nuclear phenomenon

Discussion

19.	Radioactive decay is an example of:
Answer» FIRST ORDER SECOND order ZERO order 0.5 order ANSWER :A

Discussion

20.	Radioactive decay is a statisticle process i.e., we cannot precisely predict the timing of a particular radioactivity of a particular nucleus . The nucleus can disintegrate immediately or it may take infinite time . Simply the probability of the number of nuclei being disintegrated at any instant can be predicted . the rate at which a particular decay process in a radioactive sample is directly proportional to the number of radioactive nuclei present and thus obeys first order kinetics . the factor dN/N expresses the fraction of nuclei decayed in time dt.t_(1//2) is the time in which half of the atoms are decayed and average life is the time for the nucleus to survive before decay . 75 atoms of a radioactive species are decayed in 2 half lives (t_(1//2) =1 hr ) if 100 atoms are taken initially . Number of atoms decayed if 200 atoms are taken in 2 hr are :
Answer» 75 150 50 200 Solution :`100 OVERSET(1 hr)(to) 50 overset(1HR)(to) 25 = 75` decreases

Discussion

21.	Radioactive decay is a statisticle process i.e., we cannot precisely predict the timing of a particular radioactivity of a particular nucleus . The nucleus can disintegrate immediately or it may take infinite time . Simply the probability of the number of nuclei being disintegrated at any instant can be predicted . the rate at which a particular decay process in a radioactive sample is directly proportional to the number of radioactive nuclei present and thus obeys first order kinetics . the factor dN/N expresses the fraction of nuclei decayed in time dt.t_(1//2) is the time in which half of the atoms are decayed and average life is the time for the nucleus to survive before decay . A freshly prepared radioactive source of half period 2 hour emits radiations on intensity which is 64 times of the permissible safe level. The minimum time after which it would be possible to work with this source is :
Answer» 16 hrs 12 hrs 20 hrs 24 hrs Solution :`64 overset(1)(to) 32 overset(2) (to) 16 overset(3) (to) 8 overset(4) (to) 4 overset(5) (to) 2 overset(6) (to) 1 , t = t_(1//2) xx 6 = 2 xx 6 = 12`

Discussion

22.	Radioactive decay follows first order kinetics and the rate constant is often termed as decay constant. Certain radioactive substances may undero sequential decays in order to convert intoa stable nucleus. The series comprisingall such elements is termed asradioactive disintegration series. A radioactive series is formed such that after eachalphadecay there are two consecutive beta decay and the cycle repeats. How many different elements this series can have if there are 12 members in the series ?
Answer» 12 4 3 6 Solution :After a very long time `: lambda_(1)N_(A)=lambda_(2)N_(B)` `(N_(A))/(N_(B))=(lambda_(1))/(lambda_(2))=(4 xx 10^(-2))/(16 xx10^(-5))=(1)/(4)=10^(-7)=2.5 xx 10^(-8) `

Discussion

23.	Radioactive decay is a
Answer» SECOND ORDER reaction FIRST order reaction Zero order reaction Third order reaction Solution :Radioactive DECAYS is a first order reaction

Discussion

24.	Radioactive decay follows…..order kinetics.
Answer» Zero I II III Answer :B

Discussion

25.	Radioactive decay follows first order kinetics and the rate constant is often termed as decay constant. Certain radioactive substances may undero sequential decays in order to convert intoa stable nucleus. The series comprisingall such elements is termed asradioactive disintegration series. A substance A undergoes sequential decay as shown A overset(lambda_(1))rarr B overset (lambda_(2))rarr C. If the decay constant lambda_(1) and lambda_(2) are 4 xx10^(-2) "min"^(-1) and 16 xx 10^(5) "min" ^(-1) respectively then the molar ratio of B to A after a very long time will be :
Answer» `2.5 xx 10^(-8)` `4 xx 10^(-2)` `(1)/(16 )xx 10^(-5)` `4 xx 10^(7)` Solution :`[._(z)X^(A) underset (-alpha)rarr ._(z-2)X^(A-4)underset(-BETA)rarr ._(z-1)X^(A-4)underset(-beta)rarr ._(z)X^(A-4)` `:.` In this series there will be three will be three DIFFERENT element with ATOMIC no A, A-2, Z-1]

Discussion

26.	Radioactive decay follows first order kinetics and the rate constant is often termed as decay constant. Certain radioactive substance may undergo sequential decays in order to convert into a stable necleus The series comprising all such elements is termed as radioactive disintegration series. A radioactive series is formes such that after each alpha decay there are two consecutive beta decay and the cycle repeats How many different elements this series can have if there are 12 members in the series?
Answer» 12 4 3 6 Answer :C

Discussion

27.	Radioactive decay follows first order kinetics and the rate constant is often termed as decay constant. Certain radioactive substance may undergo sequential decays in order to convert into a stable necleus The series comprising all such elements is termed as radioactive disintegration series. If a radioactive disintegration series is observed involving only alpha and beta decays then which of the following isotopes cannot be a part of it if the parent isotope of the series is ._(91)Pa^(234)?
Answer» `._(86)Rn^(222)` `._(85)At^(216)` `._(82)Pb^(210)` `._(90)Th^(230)` Answer :B

Discussion

28.	Radioactive decay follows first order kinetics and the rate constant is often termed as decay constant. Certain radioactive substances may undero sequential decays in order to convert intoa stable nucleus. The series comprisingall such elements is termed asradioactive disintegration series. If a radioactive disintegration series is observed involving only alpha and betadecays then which of the following isotopes cannot be a part of it if the parent isotope of the series is ._(91)Pa^(234).
Answer» `._(86)Rn^(222)` `._(85)At^(216)` `._(82)PB^(210)` `._(90)Th^(230)` Solution :`[._(91)PA^(234) (4n+2) `series `._(85)At^(216) ` is not a MEMBER of (4n+2) series so it can't be a part of this series.]

Discussion

29.	Radioactive decay follows first order kinetics and the rate constant is often termed as decay constant. Certain radioactive substance may undergo sequential decays in order to convert into a stable necleus The series comprising all such elements is termed as radioactive disintegration series. A substance A undergoes sequential decay as shown A overset(lambda_(1))rarrBoverset(lambda_(2))rarr C. if the decay constant lambda_(1) and lambda_(2) are 4xx10^(-2) min^(-1)and 16xx10^(5) min^(-1) respectively then the molar ratio of B to A after a very long time will be:
Answer» `2.5xx10^(-8)` `4XX10^(-2)` `1/16xx10^(-5)` `4xx10^(7)` ANSWER :A

Discussion

30.	Radioactive carbon dating was discovered by
Answer» W.F. LIBBY G.N. Lewis J.Willard Gibbs W.Nernst Solution :For STUDIES on CARBON DATING, W.F. Libby was awarded a Nobel prize

Discussion

31.	Radioactive decay follows… order kinetics
Answer» zero I II III Solution :The rate of decay ofa radioactive SPECIES has been found to obey `- (dN)/(dt) = lambda [N]^(d)` , i.e., FIRST ORDER kinetics as studied experimentally .

Discussion

32.	Radio active Halogen is
Answer» I At Po Br Solution :At is radiacative HALOGEN

Discussion

33.	Zr and Hf have almost identical atomic radii. Give reason.
Answer» diagonal relationship SIMILAR CHEMICAL properties lanthanoid contraction similar ELECTRONEGATIVITY vlaues. ANSWER :C

Discussion

34.	Radiation used in irradation of food is
Answer» U.V. RAYS `beta-rays` `gamma-rays` all of these Answer :D

Discussion

35.	Radha and Meera are fast friends. They both study in class XII. Radha is a student of science while Meera follows commerce stream. One day, when they were playing, Radha got hurt and started Fluiding. Merra took to her house and applied some alum on the cut. The bleeding stopped immediately. (i) Why bleeding stopped when some alum is applied on the cut ? (ii) What are the values associated with Meera's decision to take Radha to her house and apply alum on her cut ?
Answer» Solution :(i) Blood is a colloidal solution of albuminoid substance. The styptic action (blood stopping action) of alum is DUE to COAGULATION of blood forming a clot which STOPS further bleeding. (ii) Values associated with Meera.s decision are : (a) Friendship (b) Keen observation (c) Applying KNOWLEDGE of chemistry to daily LIFE (d) Responsibility (e) Love and care.

Discussion

36.	Ractants rarr products Delta G = + 63 KJ "mole"^(-1) This reaction is made to take plane by coupling with
Answer» `ATP OVERSET(H_2O) ADP` `ATP overset(H_2O) rarr A` `ATP overset(H_2O) rarr AMP` `ADP overset(H_2O) rarr A` ANSWER :D

Discussion

37.	Raddish - brown (chocolate ) ppt. is formed with :
Answer» `Cu^(2+) and Fe(CN)_(4)^(4-)` `Ba^(2+)` and `SO_(4)^(2+)` `Pb^(2+)` and `I^(Θ)` NONE of these Solution :`Cu_(2)[Fe(CN)_(6)]` is chocolate colour insolublecompound

Discussion

38.	Racemisation occurs in
Answer» `S_(N)2` REACTION. `S_(N)1` reaction. Neither `S_(N)2` nor `S_(N)1` REACTIONS. `S_(N)2` reaction as well as `S_(N)1` reaction. ANSWER :B

Discussion

39.	Racemic mixture or Racemate.
Answer» Solution :A mixture containing equimolar quantities of dextro (d) and laevo (l) OPTICAL isomers which is optically inactive due to external compensation is CALLED a racemic mixture of RACEMATE. It is represented as (dl) or `(PM)`.

Discussion

40.	Racemisation is a processof
Answer» MIXING of isomers separation of isomers mixing of enantiomers separation of enantiomers Answer :C

Discussion

41.	Racemisation increases with :
Answer» Increases in stability of carbocation increases in basicity of leaving group increases in solvent POLARITY increses in activation energy of rate determining step (rds) Solution :Increases in solvent polarity , increases the LIFETIME of carbocation and stability of carbocation facilitates LONGER ATTACK from both FACE without hindrance, hence racemization more.Moreover solvent polarity decreases the ion-pair interaction also.

Discussion

42.	Racemic mixture is obtained due to halogenation of
Answer» n-pentane Isopentane neo-pentane Propane Answer :A::B

Discussion

43.	R_3SiCl on hydrolysis forms:
Answer» `R_3SiOH` `R_3Si-O-SiR_3` `R_2Si=O` NONE of the above ANSWER :B

Discussion

44.	R_(3)SiCl on hydrolysis forms
Answer» `R_(3)SiOH` `R_(3)Si-O-SiR_(3)` `R_(2)Si=O` None of these Solution :`R_(3)SICL +HOH to R_(3)SiOH +HCL` `R_(3)SiOH+HOSiR_(3) to R_(3)Si-O-SiR_(3)+H_(2)O`

Discussion

45.	R_(2)NH + HNO_(2) overset("Cold")to R_(2)N - N = O + H_(2) O Thisreaction is ,
Answer» electrophilic addtion electrophilic substitution NUCLEOPHILICADDITION NUCLEOPHILIC substitution Solution :In this REACTION`H^(+)`is REPLACEDBY `NO^(+)`. Henceitis electronphilicsubstitutionreaction .

Discussion

46.	R_(2)SiCl_(2) on hydrolysis and after that dehydration we get.
Answer» CHAIN silicones Ring silicones Both (a) and (B) NONE of these Answer :C

Discussion

47.	R_2CO to R_2CHOH. The conversion is ,
Answer» REDUCTION OXIDATION HYDROLYSIS HYDRATION ANSWER :A

Discussion

48.	R_2CH-underset(X)underset(\|)(C )-R_2 + ,B^(-) R_2C = CR_' + H - B + X^(-). This reaction is an example of
Answer» `E_1` REACTION `E_2` reaction `E_1cb` reaction FIRST ORDER reaction ANSWER :B

Discussion

49.	R_(2) CH-OH is obtained from R-MgX and what
Answer» `H-CHO` `R-COR` `R-CHO` `R-COX` ANSWER :C

Discussion

50.	R_2 NH +HNO_2 to ………..
Answer» SOLUTION :`R_2 N-N= O,H_2 O`

Discussion

Explore topic-wise InterviewSolutions in Current Affairs.

Radioactivity is a first-order process. Radioactive carbon in wood sample decays with a half-life of 5770 years. What is the rate constant (in "year"^(-1)) for the decay ? What fraction would remain after 11540 years?

Radioactive substance of 1 curie is the amount that can produce …………………………… disintegrations per second.

Radioactive substances emit gamma-rays, which are

Radioactivity is due to

Radioactive strontium as a result of radioactive fall out, is

Radioactive lead ._(82)Pb^(201) has a half-life of 8 hours. Starting from one milligram of this isotope, how much will remain after 24 hours

Radioactive isotopes that have an excessive neutron/proton ratio generally exhibit

Radioactive idoine is being used to diagnose the disease of

Radioactive distintegration is an example of

Radioactive disintegration differs from a chemical change in beings

Radioactive decay is an example of:

Radioactive decay is a

Radioactive decay follows…..order kinetics.

Radioactive carbon dating was discovered by

Radioactive decay follows… order kinetics

Radio active Halogen is

Zr and Hf have almost identical atomic radii. Give reason.

Radiation used in irradation of food is

Ractants rarr products Delta G = + 63 KJ "mole"^(-1) This reaction is made to take plane by coupling with

Raddish - brown (chocolate ) ppt. is formed with :

Racemisation occurs in

Racemic mixture or Racemate.

Racemisation is a processof

Racemisation increases with :

Racemic mixture is obtained due to halogenation of

R_3SiCl on hydrolysis forms:

R_(3)SiCl on hydrolysis forms

R_(2)NH + HNO_(2) overset("Cold")to R_(2)N - N = O + H_(2) O Thisreaction is ,

R_(2)SiCl_(2) on hydrolysis and after that dehydration we get.

R_2CO to R_2CHOH. The conversion is ,

R_2CH-underset(X)underset(|)(C )-R_2 + ,B^(-) R_2C = CR_' + H - B + X^(-). This reaction is an example of

R_(2) CH-OH is obtained from R-MgX and what

R_2 NH +HNO_2 to ………..