Why first ionisation enthalpy of $\mathrm{Cr}$ is lower than that of $\mathrm{Zn}$ ?
${ }_{24} \mathrm{Cr}:[\mathrm{Ar}] 3 d^{5} 4 s^{1} \quad{ }_{30} \mathrm{Zn}:[\mathrm{Ar}] 3 d^{10} 4 s^{2}$
After loss of one element, $\mathrm{Cr}$ attains stable $\left(d^{5}\right)$ configuration while in zinc, the electron has to be removed from $4 s$ orbital. Hence, first ionization enthalpy of $\mathrm{Cr}$ is lower than $\mathrm{Zn}$.
For the following Assertion and Reason, the correct option is
Assertion : For hydrogenation reactions, the catalytic activity increases from Group $5$ to Group $11$ metals with maximum activity shown by Group $7-9$ elements.
Reason : The reactants are most strongly adsorbed on group $7-9 $ elements.
The trivalent ion having largest size in following is
Which one of the following statements shows the correct percentage of carbon in steel, pig iron and wrought iron
Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points:
$(i)$ electronic configurations,
$(ii)$ oxidation states,
$(iii)$ ionisation enthalpies, and
$(iv)$ atomic sizes.
The transition metal having highest $3^{\text {rd }}$ ionisation enthalpy is :