Match List I (Chemical Name) with List II (Chemical Formula): A. Washing soda; B. Baking soda; C. Bleaching powder; D. Gypsum. List II: 1. CaOCl2; 2. NaHCO3; 3. Na2CO3.10H2O; 4. CaSO4.2H2O.
- (a)4 2 1 3
- (b)4 1 2 3
- (c)3 1 2 4
- (d)3 2 1 4
Correct — D, the order 3 2 1 4 (A-3, B-2, C-1, D-4). Washing soda is hydrated sodium carbonate Na2CO3.10H2O (3); baking soda is sodium bicarbonate NaHCO3 (2); bleaching powder is calcium oxychloride CaOCl2 (1); and gypsum is hydrated calcium sulphate CaSO4.2H2O (4). Reading A-B-C-D gives 3-2-1-4, which is option (d).
- (a)4 2 1 3 — This wrongly gives washing soda the gypsum formula CaSO4.2H2O (4) and gypsum the washing-soda formula Na2CO3.10H2O (3). Washing soda is a sodium carbonate, not a calcium sulphate, so 4 and 3 are swapped.
- (b)4 1 2 3 — This mislabels washing soda as CaSO4.2H2O (4), baking soda as CaOCl2 (1) and bleaching powder as NaHCO3 (2) — three wrong pairings. Only gypsum ends near right but even it is shifted.
- (c)3 1 2 4 — This gets washing soda (3) and gypsum (4) right but swaps the middle pair: it calls baking soda CaOCl2 (1, actually bleaching powder) and bleaching powder NaHCO3 (2, actually baking soda).
Everyday chemical names hide the formulas. Washing soda is hydrated sodium carbonate; baking soda is sodium bicarbonate; bleaching powder is calcium oxychloride made by passing chlorine over slaked lime; gypsum is hydrated calcium sulphate. Recognising the metal (sodium versus calcium) narrows each choice fast.
Matching succeeds if you first split the four into sodium salts (washing soda, baking soda) and calcium salts (bleaching powder, gypsum). Then washing soda is the carbonate and baking soda the bicarbonate; bleaching powder carries chlorine while gypsum carries sulphate. That fixes A-3, B-2, C-1, D-4.
- Washing soda is Na2CO3.10H2O (hydrated sodium carbonate).
- Baking soda is NaHCO3 (sodium bicarbonate).
- Bleaching powder is CaOCl2 (calcium oxychloride), from chlorine on slaked lime.
- Gypsum is CaSO4.2H2O (hydrated calcium sulphate); heating it gives Plaster of Paris.
- Swapping washing soda (carbonate) and baking soda (bicarbonate).
- Mixing bleaching powder (calcium, chlorine) with a sodium salt.
- Forgetting gypsum carries sulphate, not carbonate.
NDA/UPSC match everyday chemical names to formulas — anchor on the metal and the anion (carbonate, bicarbonate, chloride, sulphate) to pair them.
Consider the following statements: 1. Anhydrous sodium carbonate is commonly known as baking soda 2. Baking soda is used in fire extinguishers 3. Bleaching powder is manufactured in Hasenclever plant. Which of the statements given above is/are correct?
- (a) 1, 2 and 3
- (b) 2 and 3
- (c) 3 only
- (d) 1 and 2
Answer(b) 2 and 3
Same household-chemistry ground. It hinges on knowing that anhydrous sodium carbonate is washing soda, not baking soda — the very washing-soda/baking-soda distinction this NDA matching item rewards.
Match List I with List II: I. Blue vitriol II. Epsom salt III. Baking soda IV. Caustic soda; A) Sodium bicarbonate B) Sodium hydroxide C) Magnesium sulphate D) Copper sulphate.
- (a) I-C, II-D, III-B, IV-A
- (b) I-D, II-C, III-A, IV-B
- (c) I-C, II-D, III-A, IV-B
- (d) I-D, II-A, III-B, IV-A
Answer(b) I-D, II-C, III-A, IV-B
The identical skill — matching trivial names (blue vitriol, Epsom salt, baking soda, caustic soda) to their chemical identities, exactly the trivial-name-to-formula recall this NDA question tests.
- practice — not a real PYQ
The chemical formula of baking soda is
- (a)Na2CO3.10H2O
- (b)NaHCO3
- (c)CaOCl2
- (d)CaSO4.2H2O
Answer(b) NaHCO3 — baking soda is sodium bicarbonate; washing soda is the carbonate.
- practice — not a real PYQ
Gypsum on heating to about 100 degrees C gives
- (a)Washing soda
- (b)Bleaching powder
- (c)Plaster of Paris
- (d)Quicklime
Answer(c) Plaster of Paris — partial dehydration of gypsum (CaSO4.2H2O) gives Plaster of Paris (CaSO4.1/2H2O).