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General ScienceMediumAsked in: CDS · CDS-I 2023, GK

Which one of the following is the correct order of pH for the given substances?

  1. A.Coffee < Lemon juice < Milk of magnesia < Blood
  2. B.Milk of magnesia < Blood < Coffee < Lemon juice
  3. C.Lemon juice < Blood < Coffee < Milk of magnesia
  4. D.Lemon juice < Coffee < Blood < Milk of magnesia

Correct answer

D. Lemon juice < Coffee < Blood < Milk of magnesia

Explanation

The correct answer is D, Lemon juice < Coffee < Blood < Milk of magnesia. Arranged from most acidic to most basic, the four substances fall in exactly this order.

Lemon juice, rich in citric acid, has a pH of about 2 to 2.5. Black coffee is mildly acidic at about 5. Human blood is slightly basic and is held within a narrow range of about 7.35 to 7.45. Milk of magnesia, a suspension of magnesium hydroxide used as an antacid, is clearly basic at about 10.5. The lower the pH, the more acidic the substance; 7 is neutral.

A is wrong because coffee is less acidic than lemon juice, and milk of magnesia is more basic than blood. B is wrong because it reverses the order, running from basic to acidic. C is wrong because it places blood, which is basic, below coffee, which is acidic.

Exam tip: lemon about 2, coffee about 5, blood about 7.4, milk of magnesia about 10.5.

Practice Questions

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Q1.General ScienceAsked in: CDS · CDS-I 2023, GKMedium

Which one of the following is not true for anodizing process?

  1. A.It makes aluminium corrosion resistant.
  2. B.Metals like aluminium, titanium and magnesium can be anodized.
  3. C.Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
  4. D.It is used in aircraft industry.
Show answer
Correct answer: C. Clean aluminium article is the anode and oxygen gas is evolved at the cathode.

In anodizing the clean aluminium article is indeed the anode, but oxygen is released at the anode, not at the cathode; hydrogen is released at the cathode.

Q2.General ScienceAsked in: CDS · CDS-II 2016, GKMedium

Which one of the following statements is not correct?

  1. A.The response of the ear to sound of increasing intensity is approximately logarithmic.
  2. B.The sensitivity of the human ear does not vary with the frequency of the sound.
  3. C.When two or more waves traverse the same medium, the displacement of any element of the medium is the algebraic sum of the displacements due to each wave.
  4. D.Longitudinal waves can travel in all media—solids, liquids and gases.
Show answer
Correct answer: B. The sensitivity of the human ear does not vary with the frequency of the sound.

The statement that the sensitivity of the human ear does not vary with frequency is false, because the ear is far more sensitive to some frequencies than to others.

Q3.General ScienceAsked in: CDS · CDS-I 2017, GKEasy

Kwashiorkor disease in children is caused by

  1. A.sufficient carbohydrates but less fats in diet
  2. B.sufficient carbohydrates and fats but deficient proteins in diet
  3. C.sufficient vitamins but deficient fats in diet
  4. D.sufficient fats but deficient vitamins in diet
Show answer
Correct answer: B. sufficient carbohydrates and fats but deficient proteins in diet

Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.