Question

The lightest chemical elements is/are:
(A) Hydrogen
(B) Helium
(C) Both a and b
(D) Oxygen

Answer 1

Hint: The lightest elements present are hydrogen, helium, lithium and beryllium.

Complete step by step answer:
In the periodic table, the lightest element can be determined from their atomic number. If a chemical element has an atomic number of 10, they are more massive than the chemical element with atomic number 5. Thus, the periodic table gives the clear picture of lightest and heaviest elements.
Hydrogen has an atomic number and atomic mass of 1 and Helium has an atomic number of 2 with atomic mass of approximately 4 amu.
The lightest chemical elements are hydrogen and helium.
So, the correct option is C.

Additional Information: Hydrogen is the lightest and most common element in the universe. It is employed as rocket fuel due to high efficiency. Hydrogen was originally formed in the big bang and is part of the fusion process that powers stars like our Sun. This is the only element that exists without neutrons.Pure hydrogen is not easily found on the Earth but can be obtained from hydrocarbons. Helium is the second most abundant element. This element is so light that even earth’s gravity is not strong enough to hold it. Thus, they easily escape into the air. It was first found in the Sun's atmosphere.

Note: Atomic number gives the number of protons present in the chemical element. Atomic mass is the sum of protons and neutrons present in the nucleus which gives the relative atomic mass.