(a) Define the following terms:
(i) Valency, (ii) Atomic size
(b) How do the valency and the atomic size of the element vary while going from left to right along a period in the modern periodic table?

Explanation

### Step-by-Step Text Solution

#### (a) Definitions

**(i) Valency**:
Valency is defined as the number of electrons that an atom can gain, lose, or share in order to achieve a stable electronic configuration, typically that of a noble gas. For example, fluorine has an electronic configuration of \(1s^2 2s^2 2p^5\). To achieve the stable configuration of neon, which is \(1s^2 2s^2 2p^6\), fluorine needs to gain one electron. Therefore, the valency of fluorine is 1.

**(ii) Atomic Size**:
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