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General ScienceMediumAsked in: NDA · NDA-I 2025, GAT

Element X forms a chloride with the formula XCl 2 , which is a solid with high melting point. X would most likely be in the same group of periodic table as

  1. A.Na
  2. B.Al
  3. C.Mg
  4. D.K

Correct answer

C. Mg

Explanation

The correct answer is C, Mg. A chloride XCl2 means X has valency 2, and an ionic chloride with a high melting point points to a Group 2 metal such as magnesium.

Elements of Group 2, the alkaline earth metals (Be, Mg, Ca, Sr, Ba), have two electrons in the outermost shell. They lose both to form X2+ ions, which combine with two chloride ions to give MCl2, for example MgCl2 and CaCl2. These are ionic solids held by strong electrostatic forces, so they melt at high temperatures. The formula and the ionic nature together fix the group.

A is wrong because sodium, in Group 1, forms NaCl with valency 1.

B is wrong because aluminium, in Group 13, forms AlCl3, which is largely covalent and sublimes at a low temperature.

D is wrong because potassium is also in Group 1 and forms KCl.

Exam tip: Group 1 gives MCl, Group 2 gives MCl2, Group 13 gives MCl3.

Practice Questions

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

A charged particle moves through a magnetic field B with a velocity v. Which one of the following statements is true for the force (F) experienced by the particle?

  1. A.F is maximum when v and B are parallel to each other.
  2. B.F is maximum when v and B are anti-parallel to each other.
  3. C.F is maximum when v and B are perpendicular to each other.
  4. D.The force F is independent of the angle between v and B.
Show answer
Correct answer: C. F is maximum when v and B are perpendicular to each other.

The magnetic force depends on the sine of the angle between velocity and field, and sin 90° is the largest value.

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

Which one of the following is the most characteristic property of an element?

  1. A.Density
  2. B.Boiling point
  3. C.Mass number
  4. D.Atomic number
Show answer
Correct answer: D. Atomic number

The number of protons in the nucleus defines an element, and no two elements share it. The atomic number (Z) is the number of protons in an atom's nucleus, and in a neutral atom it also equals the number of electrons, which decide chemical behaviour.

Q4.General ScienceAsked in: CDS · CDS-II 2017, GKHard

After using for some time, big transformers get heated up. This is due to the fact that

1. current produces heat in the transformers

2. hysteresis loss occurs in the transformers

3. liquid used for cooling gets heated

Select the correct answer using the code given below.

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

A transformer heats up because of energy lost inside it: heat from current in the windings and hysteresis loss in the iron core.

Q5.General ScienceAsked in: CDS · CDS-I 2018, GKEasy

Statement I : A person may suffer from tuberculosis if she/he frequently visits crowded place.

Statement II : Bacteria of tuberculosis spread through droplets by sneezing or coughing.

  1. A.Both the statements are individually true and Statement II is the correct explanation of Statement I
  2. B.Both the statements are individually true but Statement II is not the correct explanation of Statement I
  3. C.Statement I is true but Statement II is false
  4. D.Statement I is false but Statement II is true
Show answer
Correct answer: A. Both the statements are individually true and Statement II is the correct explanation of Statement I

Both statements are true, and the airborne spread of the TB bacterium is exactly why crowded places raise the risk.