Answer
See explanation below.
Work Step by Step
a.If Z> 83, the nuclides undergo alpha decay.
b.The N/Z ratio for Cr-48 is 24/24=1, This is below the stability band. To become stable the nuclei should undergo positron decay or through electron capture.
c.The N/Z ratio for Mn-50 is 25/25=1, This is below the stability band.To become stable the nuclei should undergo positron decay or through electron capture.