Answer:

a. **Isobars:**

Isobars are atoms of different elements that have the same mass number (total number of protons and neutrons) but different atomic numbers. This means they belong to different chemical elements but have the same overall atomic mass.

b. **Element Y:**

i. **Electronic configuration:**

The atomic number of Y is 17.

Electronic configuration: \(1s^2 2s^2 2p^6 3s^2 3p^5\)

ii. **Number of valency electrons in Y:**

The number of valency electrons is the number of electrons in the outermost shell, which is 5 in the case of Y.

iii. **Electrons needed to complete the octet of Y:**

Y needs 3 more electrons to complete its octet (8 electrons in the outermost shell).

iv. **Metal or non-metal:**

Y is a non-metal.

c. **Valency of Na:**

The valency of an element is the number of electrons an atom can lose, gain, or share to achieve a stable, noble gas electron configuration.

Sodium (Na) has an atomic number of 11, and its electronic configuration is \(1s^2 2s^2 2p^6 3s^1\). It has one electron in its outermost shell, and to achieve a stable configuration similar to noble gases, it tends to lose this electron. Hence, the valency of Na is 1, not 7. This behavior is based on achieving a stable octet (8 electrons in the outermost shell).

Answer:

a. **Isobars:**

Isobars are atoms or ions of different elements that have the same mass number but different atomic numbers. In other words, they have the same total number of protons and neutrons but different numbers of protons.

b. **Element Y:**

i. **Electronic Configuration:** 1s² 2s² 2p⁶ 3s² 3p⁵

ii. **Number of Valency Electrons:** 7 (Outermost shell - 3s² 3p⁵)

iii. **Electrons Needed to Complete Octet:** 1 (to reach a stable octet)

iv. **Metal or Non-metal:** Y is a non-metal.

c. **Valency of Na:**

The valency of an element is related to its ability to gain or lose electrons to achieve a stable electron configuration. Sodium (Na) has an atomic number of 11 and electron configuration 1s² 2s² 2p⁶ 3s¹. It tends to lose one electron to achieve a stable electron configuration similar to noble gases, and this results in a val

ency of 1. The valency is related to the outermost electron shell, and for sodium, it's easier to lose one electron than to gain seven.