The mass number of an element is equal to the number of __________.
Protons + Neutrons
An atom has a small nucleus containing protons and neutrons (together called nucleons), with electrons moving around it. Almost the entire mass of the atom lies in the nucleus because an electron is about 1/1836 the mass of a proton.
The mass number A is defined as the total number of nucleons, that is A = number of protons + number of neutrons. For example, carbon-12 has 6 protons and 6 neutrons, giving mass number 12.
The number of protons alone is the atomic number Z; the number of neutrons alone is A − Z; electrons are not counted because they contribute negligible mass and are outside the nucleus.
Protons + Neutrons option is correct.
Important Questions from Structure of Atom
- How many moles of He atoms are present in its 20 u mass ?
Which of the following electron transition in hydrogen atom will require largest amount of energy?
A species having 8 electrons in the third shell is very reactive while the other species having 8 electrons in the third shell is very inactive they are :
Which of the following is the general formula for saturated hydrocarbons?
Which one of the following is the average atomic mass of chlorine atom?
