An element X has atomic number 35. Answer the following questions.

(a) State the period and group to which it belongs.

(b) It is a metal or non-metal?

(c) Write a formula between X and hydrogen.

(a) The element belongs to group 17 and period 4.
Reason — The element X has atomic number 35 and so the electronic configuration will be 2, 8, 18, 7. The number of shells present in an atom determines it's period. Hence, Z will belong to 4th period as it has four shells. The number of valence electrons determines the group and as 7 electrons are present in valence shell hence the element will be in group 17.

(b) It is a non-metal.

(c) HX

Step 1 — Write each symbol with its valency

$\text{H}^{1+} \phantom{\nearrow} \text{X}^{1-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{X}} \Rightarrow \underset{\phantom{1}{1}}{\text{H}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{X}} \\[0.5em]$

Step 3 — Write the interchanged number, ignore equal numbers & hence the formula is : $\bold{HX}$