Fewpal
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The 1st , 2nd and the 3rd ionization enthalpies I1, I2 and I3, of four atoms with atomic numbers n, n+1, n+2 and n+3 , where n < 10, are tabulated below. What is the value of n?

Atomic numberIonization Enthalpy (kJ/mol)
I1I2I3
n168133746050
n + 1208139526122
n + 249645626910
n + 373814517733

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1 Answer

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Answer: 9

Atomic numberIonization Enthalpy (kJ/mol)
I1I2I3
n168133746050
n + 1208139526122
n + 249645626910
n + 373814517733

By observing the values of I1, I2 & I3 for atomic number (n+2), it is observed that I2 >>I1. This indicates that number of valence shell electrons is 1 and atomic number (n+2) should be an alkali metal. 

Also for atomic number (n+3), I3 >> I2

This indicates that it will be an alkaline earth metal which suggests that atomic number (n+1) should be a noble gas & atomic number (n) should belong to Halogen family. Since n < 10; hence n = 9 (F atom) 

Note : n = 1 (H atom) cannot be the answer because it does not have I2 & I3 values.

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