Question

An atom has 7 electrons in its M - shell and contains 18 neutrons in its nucleus. What is its mass number

• A. 22
• B. 30
• C. 35
• D. 45

Answer 1

The correct option is C 35

According to the Bohr model, Each shell can occupy 2n2n2 electrons in their orbits where n=1,2,3.. for K, L, M,

The atom has 2 electrons in k, 8 electrons in L and 7 electrons in M = 2 + 8 + 7 = 17

And given that its nucleus has 18 neutrons

its mass number = number of (electrons + neutrons ) = 17 + 18 = 35

so answer is option C