Question

If m, m_n and m_p are the masses of nucleus, neutron and proton respectively of ZXA nucleus, then:
1. m = (A-Z)m_n + Zm_p
2. m < (A-Z)mn + Zmp
3. m > (A-Z)mn + Zmp
4. m < Zmn + (A-Z)mp

Answer 1

Correct Answer - Option 2 : m < (A-Z)mn + Zmp

CONCEPT:

Mass defect:

• The actual mass of the nucleus is less than the sum of individual masses of the constituent neutrons and protons because energy is ejected when the nucleus is created.
• This energy consists of mass which is ejected from the total mass of the original components of the nucleus is called a mass defect.

​EXPLANATION:

In the element ZX^A,

⇒ Z = number of protons

⇒ A = mass number of element

So,

⇒ A - Z = number of neutrons

• The actual mass of the nucleus is less than the sum of individual masses of the constituent neutrons and protons because energy is ejected when the nucleus is created.

So,

⇒ m < (A-Z)mn + Zm_P

• Hence, option 2 is correct.