A radioactive nucleus a series of decays according to the scheme
`A underset rarr (alpha) A_(1) underset rarr (beta) A_(2) underset rarr (alpha)A_(3) underset rarr(gamma) A_(4)`
If the mass number and atomic number of `A `are `180` and `72`, respectively, then what are these number for `A_(4)` ?

Options

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

Answer

A

Explanation

Two `alpha`-particles reduce mass number by `8 `.
Therefore, new mass number `=180 -8=172`
Emission of two `alpha`-particles reduces charge number by `4`.
Emission of `beta`-particles increases charge number by `1`.
Therefore the new charge number `=72-4+1=69`.