If `._(92)U^(238)` changes to `._(85)At^(210)` by a series of `alpha`-and `beta` -decays, the number of `alpha` and `beta`-decays undergone is .

Options

A. `7 and 5`
B. `7 and 7`
C. `5 and 7`
D. `7 and 9`

Answer

b

Explanation

Let number of `alpha`-decays are x and number of `beta`-deacys are y. Then,
`92-2x+y=85`
or `2x-y=7`
and `238-4x =210`
`:. X=7`
Substitiing this value in Eq. (1)we, get y=7 .