Question

If ${}_{12}^{25}A$ and ${}_{18}^{40}B$ are two elements, which of the following are correct about them?

• A. Mass number of B is 40
• B. Mass number of A is 25
• C. Mass number of A is 12
• D. Atomic number of B is 18

Answer 1

Answer: (A), (B), (D)

Atomic number of B is 18

An element X is represented as ${}_Z^{A}X$, where 'Z' is the atomic number and 'A' is the mass number. So, for the given options -
$$\begin{array}{ccc}\text{Element}& \text{Atomic no.}& \text{Atomic mass no.}\\ \text{A}& \text{12}& \text{25}\\ \text{B}& \text{18}& \text{40}\end{array}$$