Question

Relative atomic mass of calcium is approximately ________ its atomic number.
A.Equal
B.Twice
C. Thrice
D. None of these

Answer 1

Hint: Relative atomic mass is the average mass of the atom when compared with $1/{12^{th}}$ mass of atom of carbon-12. Relative atomic mass is also known as atomic mass. The number of protons in an atom indicates the atomic number of an atom.

Complete step-by-step answer:
To solve the question, we must know the atomic number and mass number of calcium. Then, we will compare the mass number and atomic number of calcium.

Atomic mass indicates the number of protons. Atomic number of Calcium $\left( {{\rm{Ca}}} \right)$ is 20. So, there are 20 protons in calcium. Summation of protons and neutrons gives us the mass number. Number of neutrons in calcium is 20. As 20 neutrons and 20 protons are present, so, the mass number of calcium is 40. The atomic mass is 40 and the atomic number of calcium is 20. So, atomic mass of calcium is two times than its atomic number.
Hence, the correct option is B.

Additional Information: An atom has three subatomic particles, neutron, proton and electron. Proton has charge of +1 and electron has charge of -1 and neutron is neutral. The atomic gives the proton number in an atom. The addition of number of neutrons and protons gives the atomic mass of the atom.

Note: An element is represented by the chemical symbol of the element, its mass number and the atomic number, such as, ${}_{\rm{Z}}^{\rm{A}}{\rm{X}}$, where, X is the chemical symbol, A is the mass number and Z is the atomic number.