Question

an element X has a mass number 40 and contains 21 neutrons in its atom .To which group of periodic table does it belong?

Answer 1

no.of protons = mass no - no.of neutrons
                     =40-21
                      =19
no.of protons = no.of electrons.
1st group and 4th element is potassium-2,8,8,1

Answer 2

Answer:

Element X belongs to group one of the periodic table.

Explanation:

What is the mass number?

The sum of the number of protons and neutrons of an atom is called the mass number.

Given:

The mass number of X:40

Number of neutrons:21

Solution:
Mass number=Neutrons+Protons

∴Protons=Mass number-Neutrons

=40-21

=19

Therefore, the electronic configuration of X is 2,8,8,1.

X has one electron in the last shell.

The last shell with one electron is the characteristic property of group one elements.

Therefore, element X belongs to group one of the periodic table.