Question

An atom has mass number A and atomic number Z.

1. How many protons are present in the nucleus?
2. How many electrons are revolving around the nucleus?
3. How many neutrons are present in its nucleus?

Answer 1

(i) Protons are present in the nucleus

• Atomic number is the number of protons present in an atom.
• Atomic number= Z (Given)
• Therefore, the number of protons present in the nucleus in an atom= Z

(ii) Electrons revolving around the nucleus

• In an electrically neutral atom, Number of electrons= Number of protons
• And, Number of protons= Z [from (i)]
• Therefore, Number of electrons = Z

(iii) Neutrons present in its nucleus

• Mass number of an atom is the sum total of the number of protons and number of neutrons.
• Mass number= Number of protons+ Number of neutrons
• Therefore, Number of neutrons= Mass number- Number of protons
• Mass number= A (Given)
• Number of protons= Z [from (i)]
• Number of neutrons= A -Z