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The critical angle for glass-air interface is-

42^o

• Catenation is shown by both Silicon and Carbon. 
• Silicon bonds are less stable and reactive whereas bonds formed by Carbon bonds are very strong hence carbon shows better catenation than Silicon.

Yes, virtual image can be photographed by a camera

(c) total internal reflection.

Carbon forms strong bonds among themselves and with other elements and this makes the carbon compounds stable whereas silicon shows catenation property due to which it forms compounds with hydrogen having chains of up to 7 or 8 silicon atoms; but due to weak bonds, these compounds are unstable.

Light chooses the path which takes the least time to travel.

Angle to the mirror surface=40° 

Therefore, angle of incidence= 90° -40° =50° 

According to the second law of reflection, angle of incidence is equal to the angle of reflection. Therefore, angle of reflection=50°  

(d) both (b) and (c).

According to the second law of reflection, angle of incidence is equal to the angle of reflection. Therefore, angle of reflection=30°

(a) angle of incidence = 0° (b) angle of reflection = 0°

(c) equal to the angle of emergence.

The total deviation produced in the path of ray is 120°.

Angle of incidence, i = 0° 

Angle of refraction, r = sin (i)×n 

Where n = refractive index 

So, r₁ = 0° 

Where, 

r₁ = angle of refraction at PQ 

r₂ = angle of incidence from inside on side PR 

A = angle of prism 

We know that 

A = r₁ + r₂ 

r₂ = A – r₁ 

= 60° – 0° 

= 60°

If the angle made by the incident ray with the surface of a plane mirror is 30°, the angle of reflection must be 60°.

If the angle of incidence is 20°, the angle made by the reflected ray with the normal to the surface must be 20°.

When light is reflected, the angles of incidence and reflection are Equal.

If the angle of incidence is 40°, the angle made by the reflected ray with the surface of the plane mirror must be 50°.

(i) Angle of emergence = angle of incidence. 

(ii) Angle of deviation becomes minimum in this situation.

Correct option is B) Reflected ray

Correct option is D) incident ray

C) be parallel to the principal axis

Light always choose the path of least time to travel.

Correct option is B) Reflected ray

Plane touching the heads of pins and parallel to the plane of paper.

Reflected ray will make some angle with plane of the paper.

Some part of light is reflected and remaining part is partly transmitted or partly absorbed.

Curved reflected surfaces.

The rays coming parallel to principal axis after reflection diverge from the mirror. So we cannot burn a paper by using a convex mirror.

Measures to conserve forests:

• Illegal cutting of trees should be prohibited. Severe punishment should be given to guilty.
• Trees should also be grown on wasteland and people should be motivated for afforestation.
• Use of renewable energy sources such as solar energy, biogas, wind energy, etc. should be increased.
• People should be made aware of benefits of using these resources.
• More forest research institutes should be established for increasing the number of trees and expanding forests in a scientific manner.
• An atmosphere, which encourages every citizen to be responsible for protecting forests, should be created.

Converging lens

Correct option is C) Concave

C) Archimedes

(a) Calcium oxide reacts vigorously with water and releases a large amount of heat.

(b) Calcium hydroxide (Slaked lime) i.e Ca(OH)₂ is formed.

लिथियम एवं बेरीलियम धातुएँ है |

‘X’ has atomic number 17 

∴ Electronic configuration → 2, 8, 7 

(a) Valency = 1 

(b) Formula of halide = HX 

(c) Type of ion formed = Negative ion (Anion). 

(d) Reactivity = Most reactive among those elements which lie below X in a group.

(i) Valency of group 1 elements = 1

Valency of oxygen = 2

Oxides of group 1 elements :

Formula of the oxides of group 1 is M₂O, where M is the group 1 element and O is oxygen.

(ii) Valency of group 13 elements = 3

Valency of halogens= 1

Halides of group 13 elements :

Formula of the halides of group 13 is MX₃, where M is the group 13 element and X is halogen.

(iii) Valency of group 2 elements= 2

Valency of group 16 elements = 2

Compounds of group 2 and group 16 elements :

Formula of the compounds of group 2 and 16 is MN, where M is the group 2 element and N is the group 16 element.

Consider the following reaction,

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

(non metallic oxide)

Here, calcium hydroxide (Ca(OH)₂) is a base, and it reacts with carbon dioxide (CO₂) to give salt (calcium carbonate) and water. Comparing the above reaction with, 

Base + Acid → Salt + Water 

One can see that CO₂ acts as an acid. Hence, one can prove that non-metallic oxides are acidic in nature.

Sulphuric acid (H₂SO₄) is much stronger than sulphurous acid (H₂SO₃) because when sulphuric acid dissociates, it gives more number of H⁺ ions i.e. 2 whereas on dissociation, sulphurous acid gives less number of H⁺ ions i.e. 1.

Sulphuric acid is stronger than sulphurous acid because the presence of water in dilute sulphuric acid increases the hydrogen ion concentration. Hence it is a stronger acid than concentrated sulphuric acid which contains comparatively less water. 

(a) Hydrogen is oxidised to Water

(b) Copper oxide is reduced to Copper

(c) Copper oxide is the oxidising agent

1. (ii) H₂

2. (i) CuO

3. (i) CuO

4. (ii) H₂

5. (iii) Redox reaction

B) addition reaction

(i) Ethanol, (ii) Ethanal.

Correct option is  D) Acetic acid

(C) double displacement reaction

When barium sulphide reacts with zinc sulphide, a precipitate of barium sulphate is formed.

BaS + ZnSO₄ ⟶ BaSO₄ + ZnS precipitate

 Complete the following reactions.

i) CH₃ CH₂ OH \(\overset{Con.H_2SO^4}{\underset{Heat}{\longrightarrow}}\)CH₂ = CH₂ + H₂O

ii) CH₃ COOH + NaHCO₃→ CH₃ COONa + H₂O + CO₂

iii) CH₄ + Cl₂ \(\overset{Sunlight}{\underset{}{\longrightarrow}}\)CH₃ Cl + HCl

iv) CH₂ = CH₂ + H₂ \(\overset{Ni}{\underset{}{\longrightarrow}}\)CH₃ - CH₃

(i) The colour of the precipitate is yellow.

(ii) The yellow precipitate formed is barium chromate.

(iii) The type of chemical reaction is double displacement.