A redioctive nucleus decays as follows :
`Xoverset(alpha)(to)X_(1)overset(beta)(to)X_(2)overset(alpha)(to)X_(3)overset(alpha)(to)X_(4)`
If the atomic number and the mass number of X are 72 and 180 then the mass number and atomic number of `X_4` are-

Options

A. `172,70`
B. `171,69`
C. `172,69`
D. `172,68`

Answer

C

Explanation

Given in atom
`""_(z)X^(4)` , where Z = 72 and A = 180
On emission of one alpha particle atomic number decreases by two and mass number decreases by four.
On emission of one beta particle atomic number increases by two and mass number does not change. On emission of one gama particle atomic number remains same and mass number also remain same. thus for `X_4`
`A. = A - 2 xx 4 = 180 - 8= 172`
` Z.=Z-2xx2 +1xx1= 72 - 4+1 = 69 `