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General ScienceEasyAsked in: NDA · NDA-I 2020, GAT

The number of maximum electrons in N Shell is

  1. A.2
  2. B.8
  3. C.18
  4. D.32

Correct answer

D. 32

Explanation

The correct answer is D, 32. The N shell is the fourth shell (n = 4), and a shell can hold at most 2n² electrons, which gives 2 × 16 = 32.

Electron shells are named K, L, M and N for n = 1, 2, 3 and 4. The Bohr-Bury rule sets their capacities with the formula 2n²: K holds 2, L holds 8, M holds 18 and N holds 32. The N shell can hold 32 because it has four subshells, s, p, d and f, with room for 2, 6, 10 and 14 electrons. A further rule says the outermost shell of an atom cannot carry more than eight electrons, which is why the N shell fills completely only in heavy elements.

A, 2, is the capacity of the K shell (n = 1).

B, 8, is the capacity of the L shell (n = 2), and also the limit for any outermost shell.

C, 18, is the capacity of the M shell (n = 3).

Exam tip: K 2, L 8, M 18, N 32, all from 2n².

Practice Questions

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Q1.General ScienceAsked in: UPSC CAPF · CAPF 2019, Paper IMedium

The principle involved in paper chromatography is

  1. A.Absorption
  2. B.Partition
  3. C.Solubility
  4. D.Volatility
Show answer
Correct answer: B. Partition

Paper chromatography separates substances because each one divides, or partitions, itself differently between two liquid phases. In paper chromatography the stationary phase is the water held in the cellulose fibres of the paper, and the mobile phase is the solvent that rises up the paper by capillary action.

Q3.General ScienceAsked in: UPSC CAPF · CAPF 2019, Paper IEasy

Which one of the following is NOT a luminous object ?

  1. A.Sun
  2. B.Electric lamp
  3. C.Candle
  4. D.Moon
Show answer
Correct answer: D. Moon

The Moon gives out no light of its own; it only reflects sunlight, so it is a non-luminous object. A luminous object produces and emits its own light, while a non-luminous object is seen only because it reflects light falling on it.

Q4.General ScienceAsked in: UPSC CAPF · CAPF 2023, Paper IMedium

In experiment #1, a bar magnet is moved towards a conducting wire loop axially, with the magnet's north pole facing the loop. In experiment #2, the same process as in experiment #1 is repeated except that the south pole of the magnet faces the loop. Which one of the following statements is true in this context?

  1. A.The direction of current in the loop will be of opposite nature in both the experiments.
  2. B.The direction of current in the loop will be the same in both the experiments.
  3. C.No current will flow in either of the two experiments.
  4. D.More current will flow in the loop in experiment #1.
Show answer
Correct answer: A. The direction of current in the loop will be of opposite nature in both the experiments.

Reversing the pole that approaches the loop reverses the change in magnetic flux, so the induced current reverses too. When a magnet moves towards a closed loop, the magnetic flux through the loop changes and an electric current is induced (Faraday's law of electromagnetic induction).

Q5.General ScienceAsked in: NDA · NDA-I 2018, GATMedium

Which one of the following statements about classification of plants is correct?

  1. A.Thallophytes have well differentiated body design
  2. B.Funaria is a fungus
  3. C.All Pteridophytes are Phanerogams
  4. D.Vascular system is not found among Bryophytes
Show answer
Correct answer: D. Vascular system is not found among Bryophytes

Mosses and liverworts have no xylem or phloem, so water moves through them cell to cell. Bryophytes, such as Funaria (a moss) and Marchantia (a liverwort), are called the amphibians of the plant kingdom because they live on land but need water for fertilisation.