From the figure:

Atomic number can be determined as 8. As the nucleus shows 8 protons also it can be determined because of the 8 electrons in the orbits.

Mass number is 8 + 10 = 18. Because there is written 10n which is 10 neutrons.

Valency can be determined by electronic configuration that is: 2, 6

So the valency is 2 because 2 electrons are required to complete the octet.