Atomic radius in a transition series does not vary much while that of s and p-block does. Why?

Name a transition element which does not exhibit variable oxidation states.

Why does Zr and Hf exhibit similar properties?

Why do the transition elements exhibit higher enthalpies of atomisation?

Why is the following electronic configuration not correct for the ground state of Mo atom? (at. no. = 42).
1s² 2s² 2p⁶ 3s²3p⁶3d¹⁰ 4s² 4p⁶ 4d⁴ 5s².