A uranium nucleus `._(92)U^(238)` emits and `alpha`-particle and a `beta`-particle in succession. The atomic number and mass number of the final nucleus will be

Options

A. 90, 233
B. 90, 238
C. 91, 234
D. 93, 238

Answer

C

Explanation

When a radioactive nucleus emits an `alpha-` particle (a helium nucleus `""_(2)He^(4)`), its mass number decreases by 4 while the atomic number decreases by 2.
When a radioactive nucleus emits a `beta-` particle (an electron, `e^(-)`) its mass number remains unchanged while the atomic number increases by 1.
`therefore ""_(92)U^(283)overset(alpha)rarr ""_(90)^Th^(234) overset(beta)rarr ""_(91)Pa^(234)`