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Question

An electromagnetic radiation of wavelength 242 nm is just sufficient to ionise a sodium atom. Calculate the ionisation energy of sodium in kJ/mol?

A
494.5
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B
594.5
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C
694.5
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D
794.5
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Solution

The correct option is D 494.5
From E=hv or hc/λ
We have
λ=242nm
=242×109m
c=3×108m/s
h=6.62×1034 Js

Now putting these values in the equation, we get

E1=(6.62×1034Js×3×108m/s)(242×109m)
=0.0821×1017J/atom

En=E1×NA×11000=(0.082×1017)×6.022×1023(1000)
=494.1 kJ/mol

Hence, option A is correct .

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