Answer:
i) Protons and neutrons
ii) Mass number = 15
iii) Atomic number= 12
Explanation: i) The atom is composed of two parts: named as nucleus which contains neutrons and protons which contributes to most of the mass and there is extra nuclear part which consists of electrons which revolve around the nucleus. Thus subatomic particles are found in the nucleus of the atom are protons with positive charge and neutrons with no charge.
ii) Atomic number is equal to the number of protons or the number of electrons for a neutral atom and is specific to a particular element.
Mass number is the sum of number of protons and the number of neutrons.
Given : atomic number of oxygen = 8 = number of protons
Number of neutrons = 7
Thus mass number = number of protons + number of neutrons = 8+7= 15.
iii) Mass number = 25
Number of neutrons = 13
Mass number = number of protons + number of neutrons
25 = number of protons + 13
number of protons= 25-13 = 12
Thus atomic number = number of protons = 12