When it is referred to as the smallest wavelength, it means longest energy as because energy is inversely proportional to wavelength.

Thus, the electron will jump from ground state to the state where energy is maximum(i.e.∞)

So, the ground state is n=1 and the state of higher energy is m=∞

A. we know that,

Therefore, we obtain,

B. As He has an atomic number 2, so Z=2.

Thus,

Therefore, we obtain,

C. As lithium has an atomic number of 3, so Z=3

Thus,

Therefore, we obtain,