Question

A monovalent anion has 10 electrons and 10 neutrons. What is the atomic and mass number of the element?

Answer 1

Answer:

ATOMIC NUMBER IS EQUAL TO THE NO OF ELECTRONS..i.e 10.WHILE MASS NO IS EQUAL TO THE SUM OF NO OF ELECTRONS OR PROTONS i.e 10+10=20

Answer 2

The atomic and mass number of the element are 9 and 19

Explanation:

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Atomic number = Number of electrons = Number of protons

Number of electrons in  ion = 18

Number of electrons in $X^-$ = 10

Number of electrons in X= Number of electrons in $X^-$  - Anionic charge = 10 - 1 = 9

Since negative ion is formed by the gain of electrons from the neutral atom and the number of electrons gained  is equal to the number of units of negative charge on the ion.

number of neutrons = 10

Thus atomic number = 9

Mass number = 9 + 10= 19

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