Which among the following is the correct composition of Borax?
- (a)Sodium, Boron, Magnesium and Hydrogen
- (b)Sodium, Boron, Oxygen and Hydrogen
- (c)Potassium, Boron, Oxygen and Hydrogen
- (d)Sodium, Boron, Nitrogen and Hydrogen
Correct — B, Sodium, Boron, Oxygen and Hydrogen. Borax is sodium tetraborate decahydrate, Na₂B₄O₇·10H₂O. Its formula contains sodium (Na), boron (B), oxygen (O) and hydrogen (H) — the hydrogen coming from the ten water molecules of crystallisation — so the correct set of elements is sodium, boron, oxygen and hydrogen.
- (a)Sodium, Boron, Magnesium and Hydrogen — Borax contains no magnesium; the fourth element alongside sodium, boron and hydrogen is oxygen, not magnesium.
- (c)Potassium, Boron, Oxygen and Hydrogen — The metal in borax is sodium, not potassium — it is sodium tetraborate, Na₂B₄O₇·10H₂O.
- (d)Sodium, Boron, Nitrogen and Hydrogen — Borax contains no nitrogen; the oxygen of the borate group and the water of crystallisation is what appears alongside sodium, boron and hydrogen.
Borax is a common boron compound, sodium tetraborate decahydrate, Na₂B₄O₇·10H₂O. It is a white crystalline salt used as a flux in metallurgy and soldering, in the borax-bead test, in glass and ceramics, and as a cleaning and water-softening agent.
Break the formula Na₂B₄O₇·10H₂O into its elements: sodium, boron and oxygen from the borate part, plus hydrogen (and more oxygen) from the ten waters of crystallisation. That gives sodium, boron, oxygen and hydrogen — no potassium, magnesium or nitrogen.
- Borax is sodium tetraborate decahydrate, Na₂B₄O₇·10H₂O.
- Its constituent elements are sodium, boron, oxygen and hydrogen.
- It is used as a flux in soldering and welding and in the borax-bead test to identify coloured metal ions.
- On strong heating it swells and then gives a clear 'borax bead' of sodium metaborate and boric anhydride.
- Assuming the metal is potassium instead of sodium.
- Forgetting that the ten water molecules supply the hydrogen in borax.
- Confusing borax (sodium tetraborate) with boric acid (H₃BO₃).
NDA/UPSC ask for the elements or formula of borax, or its use as a flux and in the borax-bead test.
No directly related past PYQ was found.
- practice — not a real PYQ
The chemical formula of borax is
- (a)H₃BO₃
- (b)Na₂B₄O₇·10H₂O
- (c)NaBO₂
- (d)Na₂CO₃·10H₂O
Answer(b) Na₂B₄O₇·10H₂O — borax is sodium tetraborate decahydrate.
- practice — not a real PYQ
Borax is widely used in metallurgy as a
- (a)reducing agent
- (b)flux
- (c)fuel
- (d)catalyst
Answer(b) flux — it dissolves metal oxides during soldering and welding to give a clean joint.