Astatine (At) is a radioactive element. Study the graph given below showing the number of protons vs the number of neutrons of radioactive nuclei.

(a) Identify the mass number of the nucleus Astatine (At).

(b) Which line on the graph (l, m, n, or q) will never pass through the position of the daughter nuclei, regardless of any number of α, β, or γ emissions?

(c) Give a reason for your choice in (b).

(a) A coin lies at the bottom of a beaker. Water is poured into the beaker upto a height of 8 cm. Calculate the shift seen in the position of the coin.
(The refractive index of water is 4/3. The width of the glass wall of the beaker is negligible.)

(b) How will the apparent depth be affected if the temperature of water is increased?

Answer the following with respect to a concave lens (L).

(a) Describe the path of the rays X and Y through the lens.

(b) Give one use of this lens.

(c) Calculate its power if the focal length of this lens is 20 cm.

The diagram given below shows a triangular prism of a certain material with fluorescent screen placed adjacent to it. The yellow light ray striking the surface ST of the prism shows a fluorescent spot at point X.

(a) Calculate the critical angle of the material of the prism for yellow colour.

(b) To move the fluorescent spot towards Y, the value of θ should be …………… [> 50, < 50 or = 50].

(c) Which direction will the florescent spot move if yellow light is replaced with indigo light? (towards Y or towards Z)