When the displacement is along the opposite direction of the force, then the work is said to be

1. zero
2. negative
3. positive
4. infinite

In a radioactive decay, the atomic number of parent nuclei is not changed. The radiation emitted will be

1. β-rays
2. γ-rays
3. α-rays
4. the atomic number is affected by all forms of radioactive decay

Assertion A ray of light passing through the centre of curvature of a concave mirror is reflected back along the same path.

Reason The incident ray, the reflected ray and the normal at the point of incidence lie on the same plane.

1. Both Assertion and Reason are true.
2. Both Assertion and Reason are false.
3. Assertion is false but Reason is true.
4. Assertion is true but Reason is false.

If temperature of medium increases, then critical angle

1. decreases
2. increases
3. zero
4. first increases then decreases