Question

The number of electrons and neutrons of an element is $18$ and $20$ respectively. Its mass number is

• A. 37
• B. 17
• C. 38
• D. 22

Answer 1

Answer: (C)

38

Answer 2

Mass no. $=$ No. of protons $+$ No. of neturons No. of protons $=$ No. of electrons $\Rightarrow$ No. of protons $=18$ $\Rightarrow$ Mass No. $=18+20=38$