In 3d series which element has highest melting point

The d-block elements with more number of unpaired e⁻ will have higher melting point. This is because, more the number of unpaired e⁻ s present , stronger will be the metallic bond formation.
Hence, the heat required to loosen the bond will be high.

${}_{26}\mathrm{Fe}:4{ \mathrm{s}}^{2}3{ \mathrm{d}}^6$
${}_{24}\mathrm{Cr}:4{ \mathrm{s}}^{1}3{ \mathrm{d}}^5$
${}_{25}\mathrm{Mn}:4{ \mathrm{s}}^{2}3{ \mathrm{d}}^5$
${}_{25}\mathrm{Ni}:4{ \mathrm{s}}^{2}3{ \mathrm{d}}^8$

Since, Cr contains highest number of unpaired e⁻ So, it has the highest melting point out of all.