Predicting the mode of Nuclear Decay

What is the most likely mode of decay for each? (problem 24.20 in Chemistry: The molecular nature of matter and change)

(a) A=238 Z=92 U

(b) A=48 z=24 Cr

(c) A=50 Z=25 Mn

I understand that the decay forUranium is by alpha decay, but How would you distinguish between b) and c)? Both of them have an equal number of protons and neutrons. I know that c) is unstable, compared to b...