MCQ
Atomic number of elements represent
- ✓Number of protons in the nucleus
- BNumber of neutrons in the nucleus
- CNumber of protons and neutrons in nucleus
- DThe valency of an element
For example, for ${ }_{17}^{37} Cl$, the atomic number is $17$, the mass number is $37$ , there are $17$ , electrons, $17$ protons and $37-17=20$ neutrons.
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$B.E(N -N) = 159\, kJ\, mol^{-1}$,
$B.E(H -H) = 436\, kJ\, mol^{-1}$
$B.E.(N \equiv N) = 941\, kJ\, mol^{-1}$,
$B.E(N -H) = 398\, kJ\, mol^{-1}\, .......\,kJ\, mol^{-1}$
Given : $\Delta H _{ f }^{\ominus}\left( Al _2 O _3\right)=-1700\,kJ\,mol ^{-1}$
$\Delta H _{ f }^\theta\left( Fe _2 O _3\right)=-840\,kJ\,mol ^{-1}$
Molar mass of $Fe , Al$ and $O$ are $56,27$ and $16\,g\,mol ^{-1}$ respectively.