NDA (I) 2021 GAT Q56: Which one of the following is the chemical formula of

Q: What is the answer to NDA (I) 2021 GAT Q56?

B. Correct — B, HOBr. Hypobromous acid is HOBr (also written HBrO), in which bromine is in the +1 oxidation state; the 'hypo-...-ous' name marks the least-oxygenated common oxyacid of bromine. The others are different species — HBrO₄ is perbromic acid, HBrO₃ is bromic acid, and HBr is hydrobromic acid, which contains no oxygen at all.

NDA (I) 2021 General Ability Test · Question 56 of 149

Question text verified against the official NDA question paper.

Which one of the following is the chemical formula of Hypobromous acid?

(a)HBrO₄
(b)HOBr
(c)HBr
(d)HBrO₃

Answer

Why

Correct — B, HOBr. Hypobromous acid is HOBr (also written HBrO), in which bromine is in the +1 oxidation state; the 'hypo-...-ous' name marks the least-oxygenated common oxyacid of bromine. The others are different species — HBrO₄ is perbromic acid, HBrO₃ is bromic acid, and HBr is hydrobromic acid, which contains no oxygen at all.

Why the others are wrong

(a)HBrO₄ — This is perbromic acid, with bromine in the +7 state — the most-oxygenated oxyacid, not the 'hypo-...-ous' one.
(c)HBr — This is hydrobromic acid, a hydracid with no oxygen, whereas hypobromous acid is an oxyacid that contains oxygen.
(d)HBrO₃ — This is bromic acid, with bromine in the +5 state — a higher oxyacid, not hypobromous acid.

Concept

Bromine forms a series of oxyacids that differ in the number of oxygen atoms and in bromine's oxidation state. The naming ladder runs hypo-...-ous, then ...-ous, then ...-ic, then per-...-ic in increasing oxygen — so hypobromous (HOBr, +1), bromous (HBrO₂, +3), bromic (HBrO₃, +5) and perbromic (HBrO₄, +7).

The 'hypo-...-ous' prefix-and-suffix pair always signals the least-oxygenated oxyacid. Match the name to the formula with the fewest oxygens (just one) and you arrive at HOBr.

Key facts

Hypobromous acid is HOBr (HBrO), with bromine in the +1 oxidation state.
Bromic acid is HBrO₃ (+5) and perbromic acid is HBrO₄ (+7).
Hydrobromic acid (HBr) is a hydracid — it contains no oxygen.
The oxyacid-naming ladder is hypo-...-ous, ...-ous, ...-ic, per-...-ic in increasing oxygen.

Oxyacids of bromine — name to formula

Hypobromous acid→HOBr (HBrO) — bromine +1

Bromous acid→HBrO₂ — bromine +3

Bromic acid→HBrO₃ — bromine +5

Perbromic acid→HBrO₄ — bromine +7

'Hypo-...-ous' marks the least-oxygenated oxyacid, HOBr — option (b); HBr has no oxygen at all.

Study next

Naming oxyacids (hypo-ous, -ous, -ic, per-ic)Oxidation states of halogens in their oxyacidsHydracids (HBr, HCl) versus oxyacidsOxoacids of chlorine (HOCl, HClO₂, HClO₃, HClO₄)Bleaching action of hypohalous acids

Common traps

Confusing hypobromous acid (HOBr) with hydrobromic acid (HBr) — the latter has no oxygen.
Mixing up the oxyacid ladder and picking a higher acid such as HBrO₃ or HBrO₄.

Asked as a name-to-formula match across the bromine oxyacid series — anchor on the rule that 'hypo-...-ous' has the fewest oxygens.

Related PYQs

No directly related past PYQ was found.

Practice

practice — not a real PYQ
The oxidation state of bromine in hypobromous acid (HOBr) is
- (a)−1
- (b)+1
- (c)+5
- (d)+7
Answer(b) +1 — the lowest common oxyacid state.
practice — not a real PYQ
The formula of perbromic acid is
- (a)HOBr
- (b)HBrO₂
- (c)HBrO₃
- (d)HBrO₄
Answer(d) HBrO₄ — 'per-...-ic' is the most-oxygenated oxyacid.