Question

The number of electrons in $\left[{ }_{19} K ^{40}\right]^{-1}$ is

• A. 28
• B. 19
• C. 40
• D. 20

Answer 1

Answer: (D)

20

Answer 2

Atomic No. $=19$ $e ^{-}$ present originally $=19$ total no. of $e ^{-}$ $=19+1$ (from $- ve$ $=20 \,\,\,\,\,$ charge $)$