(a) It is the case of hypermetropia.
For a hypermetropic eye, u=−25‌cm and v=−50‌cm
Using lens formula
‌‌

1

f

=‌

1

v

−‌

1

u

‌‌

1

f

=−‌

1

50

+‌

1

25

‌‌

1

f

=‌

1

50

We get focal length is f=50‌cm=0.5m
From the formula, P=‌

1

f

P=‌

1

0.5

=2D
So the power of the lens is 2 dioptre and the nature of lens is a converging lens or a convex lens.