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GUJCET 2025 Physics Paper

Question : 20 of 40

Marks: +1, -0

Which of the following pairs is called isotones?

Solution:

Concept:

Isotones are atoms of different elements having the same number of neutrons.

Explanation:

Number of neutrons is

N = A - Z

For

^{198}_{80}\mathrm{Hg}

N = 198 - 80 = 118

For

^{197}_{79}\mathrm{Au}

N = 197 - 79 = 118

Both have

118

neutrons, so they are isotones.

Option B:

^3_1\mathrm{H}

has

N=2

^3_2\mathrm{He}

has

N=1

Option C:

^{214}_{82}\mathrm{Pb}

has

N=132

^{214}_{83}\mathrm{Bi}

has

N=131

Option D:

^{12}_6\mathrm{C}

has

N=6

^{14}_6\mathrm{C}

has

N=8

; these are isotopes.

Answer:

Option A:

^{198}_{80}\mathrm{Hg}

and

^{197}_{79}\mathrm{Au}

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