Question

Which of the following atoms has no neutron in its nucleus?

• A. Helium
• B. Lithium
• C. Protium
• D. Tritium

Answer 1

Answer: (C)

Protium is the most abundant isotope of hydrogen with an abundance of almost $99\%$.
It's symbol is $H_1^1$. Its atomic number is $1$ and its mass number is also $1$.
So it does not possess any neutron.
Whereas,
Helium, $H{e}_2^4$, has $2$ neutrons
Lithium, $L{i}_3^7$, has $4$ neutrons
Tritium, $H_1^3$, has $2$ neutrons