A radioactive nucleus undergoes a series of decay according to the scheme
`A overset(alpha)rarr A_(1) overset(beta^(-))rarr A_(2) overset(alpha)rarr A_(3)^(172) overset(gamma)rarr A_4`.

Options

A. 172 and 60
B. 174 and 70
C. 172 and 69
D. 176 and 70

Answer

C

Explanation

(a) Two `alpha-`particle reduce mass number by `8`.
`:.` New mass number `= 180 - 8 = 172`
Emission of two `alpha-`particle reduces charge number by `4`. Emission of `beta` particles increases charge number by `1`.
`:.` New charge number `= 72 - 4 + 1 = 69`.