Name the element which lies in group ia and 3rd period. what is the valency of it and why?

Na, valency 1.

Explanation:

Na -sodium.

This element is in the 1A group, so it has 1 electron on the last (valent) level.

So, only 1 electron can participate in forming chemical bond, and therefore the valency of Na is 1.

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.