The correct order of the atomic radii of $\mathrm{C}, \mathrm{Cs}, \mathrm{Al}$ and S is:

(A) $\mathrm{C}<\mathrm{S}<\mathrm{Al}<\mathrm{Cs}$

(B) $\mathrm{S}<\mathrm{C}<\mathrm{Cs}<\mathrm{Al}$

(C) $\mathrm{S}<\mathrm{C}<\mathrm{Al}<\mathrm{Cs}$

(D) $\mathrm{C}<\mathrm{S}<\mathrm{Cs}<\mathrm{Al}$

JEE Main · 2019 · 11 Jan 2019 · Shift 1 · Classification of Elements and Periodicity

The correct order of the atomic radii of

C, Cs, Al

and S is:

(A) $C < S < Al < Cs$ ✓ Correct
(B) $S < C < Cs < Al$
(C) $S < C < Al < Cs$
(D) $C < S < Cs < Al$

Answer: (A)

Solution

Atomic radius falls across a period and grows down a group. Carbon, high in period 2, is the smallest. Sulphur, one period lower, is larger than carbon. Within period 3 the radius shrinks from left to right, so aluminium on the left is larger than sulphur on the right. Caesium, an alkali metal far down the table, is by far the largest. The order of increasing atomic radius is

C < S < Al < Cs

JEE Main · 2019 · 11 Jan 2019 · Shift 1 · Single correct option

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