Question

An element has atomic number 10 and an atomic mass of 20. How many neutrons are in the atom of this element? A. 10 B. 20 C. 30 D. 0 E. 200

Answer 1

Answer : The correct option is, (A) 10

Explanation :

Atomic number : It is defined as the number of protons or number of electrons.  That means,

Atomic number = number of protons = number of electrons

Atomic mass : It is defined as the sum of number of protons and number of neutrons.

Atomic mass = Number of neutrons + Number of protons

As we are given that,

The atomic number of an element = 10

The atomic mass of an element = 20

Now we have to determine the number of neutrons.

Atomic number = number of protons = 10

Atomic mass = Number of neutrons + Number of protons

Number of neutrons = Atomic mass - Number of protons

Number of neutrons = 20 - 10 = 10

Therefore, the number of neutrons are, 10