Structure of the Atom — Science STD 9 — Question

No. of electrons = 2 + 1 = 3

As we know that,

No. of proton = No. of electron

$\therefore$ No. of protons = 3

let the no. of neutrons be 'n'

As we know,

Mass of atom = no. of protons + no. of neutrons

Substituting the values, we get,

7 = 3 + n

⇒ 7 - 3 = n

⇒ 4 = n

or, n = 4

$\therefore$ No. of neutrons in the atom is 4