The metal ions that have the calculated spin-only magnetic moment value of 4.9 B.M. are :

A. $\mathrm{Cr}^{2+}$

B. $\mathrm{Fe}^{2+}$

C. $\mathrm{Fe}^{3+}$

D. $\mathrm{Co}^{2+}$

E. $\mathrm{Mn}^{3+}$

Choose the correct answer from the options given below:

The correct option with order of melting points of the pairs (Mn, Fe), (Tc, Ru) and (Re, Os) is :

The metal ion whose electronic configuration is not affected by the nature of the ligand and which gives a violet colour in non-luminous flame under hot condition in borax bead test is