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General ScienceEasyAsked in: NDA · NDA-II 2017, GAT

Which one among the following chemicals is used as washing soda?

  1. A.Calcium carbonate
  2. B.Calcium bicarbonate
  3. C.Sodium carbonate
  4. D.Sodium bicarbonate

Correct answer

C. Sodium carbonate

Explanation

The correct answer is C, Sodium carbonate. Washing soda is the crystalline form of sodium carbonate, Na2CO3·10H2O, sodium carbonate decahydrate.

Sodium carbonate is made from common salt by the Solvay (ammonia-soda) process. Heating the crystals drives off the water and gives anhydrous sodium carbonate, called soda ash. Washing soda is used to clean clothes, to remove the permanent hardness of water, and in making glass, soap and paper. Its solution is alkaline, which helps it cut grease and dirt.

A is wrong: calcium carbonate is limestone, chalk and marble, used for lime and cement. B is wrong: calcium bicarbonate exists only in solution and causes temporary hardness of water. D is wrong: sodium bicarbonate, NaHCO3, is baking soda, used in cooking and antacids, not washing soda.

Exam tip: Washing soda is Na2CO3·10H2O; baking soda is NaHCO3; bleaching powder is CaOCl2.

Practice Questions

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Q1.General ScienceAsked in: CDS · CDS-II 2020, GKEasy

The valency of phosphorus is

  1. A.2, 3
  2. B.3, 4
  3. C.4, 5
  4. D.3, 5
Show answer
Correct answer: D. 3, 5

Phosphorus has five electrons in its outer shell and shows two common valencies, 3 and 5. Phosphorus, atomic number 15, has the electronic configuration 2, 8, 5.

Q2.General ScienceAsked in: CDS · CDS-II 2026, GKMedium

Which one of the following statements is NOT correct ?

  1. A.Single celled eukaryotes belong to Kingdom Protista
  2. B.Yeast, a fungus is multicellular
  3. C.The fungi constitute a unique kingdom of heterotrophs
  4. D.Ascomycetes, a saprophytic fungi is multicellular or rarely unicellular
Show answer
Correct answer: B. Yeast, a fungus is multicellular

This statement is false, because yeast is one of the few fungi that are unicellular. In Whittaker's five-kingdom system, fungi form a separate kingdom.

Q3.General ScienceAsked in: CDS · CDS-II 2017, GKMedium

Desalination of seawater is done by using reverse osmosis. The pressure applied to the solution is

  1. A.larger than osmotic pressure
  2. B.smaller than osmotic pressure
  3. C.equal to osmotic pressure
  4. D.equal to atmospheric pressure
Show answer
Correct answer: A. larger than osmotic pressure

Only a pressure greater than the osmotic pressure of seawater can push pure water backwards through the membrane. In ordinary osmosis, water moves through a semipermeable membrane from the dilute side to the concentrated side.

Q5.General ScienceAsked in: CDS · CDS-II 2017, GKEasy

The foul smell of urine of a healthy man having healthy food, when spilled on floor, is mainly due to the bacterial decomposition of

  1. A.urea into sulphur dioxide
  2. B.sugar into carbon dioxide
  3. C.lipids into methane
  4. D.urea into ammonia
Show answer
Correct answer: D. urea into ammonia

Bacteria on the floor break down the urea in urine and release ammonia, which has a sharp, pungent smell. Urea, CO(NH2)2, is the main nitrogenous waste of humans.