An atomic nucleus A is composed of 84 protons and 128 neutrons. The nucleus A emits and alpha particle and is transformed into a nucleus B.
(i) What is the composition of B ?
(ii) The nucleus B emits a beta particle and is transformed into a nucleus C. What is the composition of C?
(iii) What is mass number of the nucleus A ?
(iv) Does the composition of C change if it emits gamma radiations ?

Explanation

Atomic number of C is one more than the mass number of B due to beta emission i.e., 82 + 1 = 83, whereas mass number remains the same i.e., 208.
`""_(82)^(208)Btoe_(-1)^(0)+""_(83)^(208)C`
So, Number of electrons in C = Number of protons in C
= Atomic number
= 83
Number of neutrons = Mass number of C - Atomic number of C
= 208 - 83 = 125