What will be the ratio of specific charge of an alpha particle to that of proton?

1:2

The specific charge is given by e/m.

The specific charge of photon = e/m_p                     ........(1)

Mass of an alpha particle = 4m_p

Charge of alpha particle = 2 × charge of single protons = 2e

The specific charge of alpha particle = 2e/4m_p = e/2m_p                    ......(2)

So from (1) and (2), the ratio will be 1:2