PLZ EXPLAIN :  mn has lower melting point than cr as

1) electrons are tightly held by nucleus in Mn (how?)

2) Mn has lower enthalpy of atomisation (why?)

The electronic configuration of Sc, Ti, V, Cr is given below:

Sc: 3d¹ 4s²  Number of unpaired electrons : 1

Ti: 3d² 4s²  Number of unpaired electrons : 2

V: 3d³ 4s²  Number of unpaired electrons : 3

Cr: 3d⁵ 4s¹  Number of unpaired electrons : 6

As the number of unpaired electron increases, the strength of metallic bond, between two metal atoms increases, which leads to increase in melting point of the metals and their enthalpy of atomisation.

Manganese's electronic configuration is 3d⁵ 4s² and, the number of unpaired electron is 5 (lesser than Cr which has 6 unpaired electron), therefore the strength of interatomic interaction in Mn, is less than that of Cr. Hence, its melting point is lower than chromium. The same is the reason for lower enthalpy of atomisation of manganese than chromium. 

Trends in enthalpies of atomisation of transition elements are shown in the given figure.

Overall, it can be summed that the melting point of transition metal is directly proportional to the number of unpaired electrons, present in its valence shell, which increases the strength of interatomic bonding, leading to increase in melting point.