Question

An element has atomic number $17$ and mass number $37$. There are $17$ electrons outside the nucleus. Find the number of neutrons in it.

• A. $20$
• B. $21$
• C. $17$
• D. $37$

Answer 1

The correct option is A $20$

$\left(A\right)$ $20$

$Given$ - Atomic number of element = $17$

Mass number of element = $37$

Number of electrons = $17$

As we know, number of protons is equal to number of electrons.

so, number of protons = $17$

now, $Massnumber$ = $numberofprotons$ + $numberofneutrons$

$37$ = $17$ + number of neutrons

number of neutrons = $37$ - $17$

number of neutrons = $20$

So, the number of neutrons in the nucleus = $20$.