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A. NO

Ozone layer is depleted by NO.

Correct answer is

C. l₂

Correct answer is

A. O

• The general outer electronic configuration of alkali metals is ns¹.
• They readily lose one valence shell electron to achieve stable noble gas configuration and hence, they are highly electropositive and are good reducing agents.

Hence,

Standard reduction potentials of alkali metals have high negative values.

• Hydrogen contains one valence electron in its valence shell and thus, its valency is one. Therefore, hydrogen resembles alkali metals (group 1 elements) as they also contain one electron in their valence shell (alkali metals tend to lose their valence electron).
• However, hydrogen also shows similarity with halogens (group 17 elements) as their valency is also one because halogens tend to accept one electron in their valence shell.
• Due to this unique behaviour, it is difficult to assign any definite position to hydrogen in the modem periodic table. 

Option : d. emerald

The family of reactive metals having valency two is known as alkaline earth metals (group 2).

The family of reactive metals having valency one is known as alkali metals (group 1).

Correct option is (a) determination of T&D needs, and evaluation of T&D programme

ClF₃ is more reactive than ClF, while BrF₅ is more reactive than BrF. Both ClF₃ and BrF₅ are unstable compared to ClF and BrF respectively due to steric hindrance hence are more reactive.

(i) SILOS (ii) THRESHING (iii) IRRIGATION (iv) RIVER 

Activity carried out in fields after maturation of crop-Harvesting

Correct option is (d) all of the above

The halogen fluorine (F) has the maximum tendency to form more interhalogen compounds as it has a small size and more electronegativity.

(i) Use of fertilisers and weedicides are hazardous to environment. Tractor causes air pollution. 

(ii) Modern agricultural implements saves on both time and labour as compared to traditional equipments. 

(iii) An example of a weedicide is 2, 4–D. Farmers should cover their mouth and nose while spraying weedicides as they can cause health hazards.

Correct option is (a) caste system

Early humans observed places where edible plants were found, about seeds, plants, etc. 

They started growing their own plants. And thus; they became farmers.

Answer is (C) nomads

Answer is (C) Fire

Answer is (A) hunting

Answer is (A) Wood

Molecular mass of polymer depends upon the degree of polymerization (DP). DP is the number of monomer units in a polymer molecule.

Molecular mass of a polymer is an average of the molecular masses of the constituent molecules.

The catalyst Zieglar Natta is formed from titanium chloride and triethyl aluminium.

Structural Features of the Modern Periodic Table

This table consists of horizontal rows called as 'periods' and vertical columns called as 'groups'.

Periods

There are seven periods in the periodic table and each period starts with a different principal quantum number.

The first period corresponding to 'n' = 1 consists of only two elements hydrogen and helium .This is because the first energy shell can accommodate only two electrons.

In the second period corresponding to 'n' = 2, with a capacity of eight electrons and so contains eight elements. This period starts with lithium (Z = 3) ends with neon (Z = 10) where the second shell is complete.

In the third period corresponding to 'n' = 3, contains eight elements. It starts with sodium (Z = 11) and ends with argon (Z = 18) where the third shell is partially complete.

The fourth period corresponding to 'n' = 4, consists of eighteen elements in this period starting from potassium (Z = 19) to krypton (Z = 36) where the third shell gets completed.

In the fifth period there are 18 elements like the fourth period. It begins with rubidium (Z = 37) and ends with xenon (Z = 54).

The sixth period contains 32 elements (Z=55 to 86) .It starts with caesium and ends with radon.

The seventh period, though expected to have 32 elements is incomplete and contains only 19 elements at present.

The first three periods are called short periods while the other three periods are called long periods.

Groups

The vertical column in the periodic table is called as group. There are 18 groups in the long form of the periodic table and they are numbered from 1 to 18 in the IUPAC system. In the old system of naming they are numbered as I to VIII with A and B groups. 

The maximum number of electrons that can be accommodated in a shell depends on the formula 2n² where 'n' is the number of the given shell from the nucleus.

For example,

K Shell - 2 x (1)² = 2, 1^st period = 2 elements.

L Shell - 2 x (2)² = 8, 2^nd period = 8 elements.

M Shell - 2 x (3)² = 18, but the outermost shell can have only 8 electrons, so the third period also has only 8 elements.

(i) False. (Chadwick discovered the neutron.)

(ii) True.

(iii) True.

(iv) False. (The capacity of the second orbit is 8 electrons.)

(v) False. (The radioactive isotope Sodium-24 is used for detection of cracks in the underground pipes.)

(vi) True.

(i) 18

(ii) 2, 7

(iii) valency one

(iv) u

The correct answer is 7 : 40 

(i) all the domains get oriented in the direction of magnetic field.

The correct answer is 2 : 3

Crop rotation : Crop rotation is policy of growing different crops one after another on the same field. 

• If some crop is grown again and again on the same field, same nutrients are extracted from soil again and again. So we should choose different crops so that all nutrients of soil are used. 

• Advantages : 

(1) Soil fertility is maintained. 

(2) It controls pests and weeds. 

(3) Several crops can be grown in succession with only one soil preparation.

The correct answer is 1 : 17

To protect crops against diseases caused organisms and other harming factors is called crop protection. 

Following methods are used to control these problems : 

(a) Pest control during growth 

(b) Storage of grains

(c) This condition will give the most benefits. Because it includes all agricultural methods. Hence yield is more.

Field crops are infested by a large number of weeds, insect pests and diseases. If weeds and pests are not controlled at the appropriate time then they can damage the crops so much that most of the crop is lost. When the crop is in the field, it needs protection against:

• Weeds e.g.– Xanthium, Parthenium (weeds are considered to be harmful as they compete for food, space and light with the desired crop. They reduce crop production taking up the nutrients meant for the crops.
• Insect Pests - 

Insect pests attack the plants in three ways: 

(i) they cut the root, stem and leaf, 

(ii) they suck the cell sap from various parts of the plant, and 

(iii) they bore into stem and fruits. They thus affect the health of the crop and reduce yields.

• Pathogens- Microbes like bacteria, fungi and viruses cause diseases. Spores of these pathogens may be transmitted through soil, water and air.

To control these :

Herbicides, Pesticides, fungicides should be used.

Weed control methods also include mechanical removal. Preventive methods such as proper seed bed preparation, timely sowing of crops, intercropping and crop rotation also help in weed control. Some other preventive measures against pests are the use of resistant varieties, and summer ploughing, in which fields are ploughed deep in summers to destroy weeds and pests.

Prevention for preventing the growth of weeds,

• Proper seed bed preparation,
• timely growing of crops,
• intercropping, crop rotation,
• use of resistant varieties and
• summer ploughing is done.

(c) Farmers using good quality seeds, adopting irrigation, using fertilizers, and using crop protection measures will derive most benefits.

(i) The use of good quality seeds increases the total crop production. If a farmer is using good quality seeds, then a majority of the seeds will germinate properly, and will grow into a healthy plant.

(ii) Proper irrigation methods improve the water availability to crops.

(iii) Fertilizers ensure healthy growth and development in plants by providing the essential nutrients such as nitrogen, phosphorus, potassium, etc.

(iv) Crop protection measures include various methods to control weeds, pests, and infectious agents. If all these necessary measures are taken by a farmer, then the overall production of crops will increase.

During his experiments on electromagnetic waves in 1887, Heinrich Rudolph Hertz (1857- 94), Ger-man physicist, noticed that electric sparks occurred more readily when one of the electrodes of his spark-gap transmitter was exposed to ultraviolet radiation. This discovery was called the Hertz effect and is now known as the photoelectric effect.

Although Hertz did not follow up his discovery, others quickly established that the cause of the sparking ease was due to emission of negatively charged particles from the electrode irradiated. These particles were identified as electrons after the discovery of the electron in 1897.

Bryophytes are differentiated into stem and leaf like structure. Thallophyta don’t have such structures and Pteridophytes are differentiated into stem and leaf.

Emission of electron from metal surface when it is subjected to high electric field (of the order of 108V) is called field emission. 

Multicellular eukaryotic organisms without cell wall are placed under kingdom Animalia. Organisms of kingdom Plantae have cell wall and the organisms of other kingdoms are unicellular.

Emission of electron from a metal surface when it is heated to sufficiently high temperature is called thermionic emission. 

In Monera kingdom will we place an organism which is single celled, eukaryotic and photosynthetic.

1eV is the energy gained by an electron when it is accelerated through a potential difference of one volt.

Chemical reduction cannot be used to prepare alkali metals since they themselves are reducing in nature. Alkali metals are highly electropositive and thus cannot be prepared by displacement reactions.

Since they also react with water, these alkali metals cannot be prepared by electrolysis of their aqueous solutions. Thus, alkali metals are mostly prepared by electrolysis of their fused chlorides.

Commerce is part and parcel of human life.

Money functions as a medium of exchange.

Commerce activities are heading for a cashless system through e-commerce which means business activities enabled through electronic modes like Online trading, Mobile banking and e – marketing.