pls ans

In O¹⁶:  mass number is 16, atomic number is 8.  Number of neutrons = 16-8 = 8
In O18, mass number is 18, atomic number is 8, number of neutrons = 18-8=10

Ratio of neutrons,

$\frac{\text{number of neutrons in} {\text{O}}^{\text{16}}}{{\text{number of neutrons inO}}^{\text{18}}}= \frac{8}{10}=\frac{4}{5}\text{(option C)}$