Question

Give reason Actual atomic mass is greater than mass number

Answer 1

actual atomic mass = mass of neutrons+ mass of protons+ mass of electrons
atomic mass=mass of neutrons + mass of protons
but the difference between them is negligible.
because mass of electrons is 1/1837 of protons

Answer 2

Explanation:

Mass number is defined as the sum of number of neutrons and number of protons present in an isotope. This is represented by 'A'.

A = Mass number = Number of protons + Number of neutrons

Actual atomic mass is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance. This is also known as average atomic mass. The equation used to calculate average atomic mass is given by:

$\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i$

This is why, actual atomic mass is always greater than the mass number of an element.