The number of electrons and neutrons in an element is 18 and 20 respectively. Its mass number is :

Explanation

The sum of the numbers of protons and neutrons present in the nucleus of an atom is called its mass number. It is noteworthy that in an atom, the number of electrons equals the number of protons; therefore, atoms are electrically neutral. As per the question: Mass number = Number of protons + Number of neutrons = 18 + 20 = 38