Mass number of an atom is the sum of its:
AProtons and neutrons
BProtons and electrons
CElectrons and neutrons
DElectrons only
Answer & Solution
Correct answer: A. Protons and neutrons
1. Mass number A counts heavy particles in the nucleus.
2. Electrons are extremely light and ignored in A.
3. So A = protons + neutrons.
4. Often written as 'A = p + n'.
_Source: Selina Concise Chemistry ICSE Class 9, Ch 4 'Atomic Structure'_
Related questions
Atomic radius is conveniently measured in which unit?Which element has three shells with 8 electrons in its outermost shell?Which sub-particle was discovered LAST?If an element has the configuration 2, 8, 8, 1, its valency and likely group are:Why does the atomic mass of chlorine (35.5) lie between two integers?An atom of oxygen has Z = 8 and A = 16. Number of neutrons is:Why are protons and neutrons together called nucleons?Isotopes of hydrogen include: