On reducing the focal length of a lens, its power :

1. decreases
2. increases
3. does not change
4. first increases then decreases.

The lens of power + 1.0 D is:

1. convex of focal length 1.0 cm
2. convex of focal length 1.0 m
3. concave of focal length 1.0 cm
4. concave of focal length 1.0 m.

If a lens is placed in water instead of air, its power :

1. increases
2. decreases
3. remains the same
4. can both increase or decrease

The focal length of a lens is (i) positive, (ii) negative. In each case, state the kind of lens.