Fill in the blanks:
$(a)$ The shielding effect of $d$-electrons is ......... effective than $p$-electrons.
$(b)$ $A$ decrease in exchange energy leads to a ......... in stability.
$(c)$ The maximum oxidation state of $Mn$ is ..........
$(d)$ The stability of $Mo(VI)$ and $W(VI)$ is found to be .......... than that of $Cr(VI)$.

• A
  Less,Decrease,+$7$,Higher
• B
  More,Increase,+$6$,Lower
• C
  Equal,No change,+$5$,Equal
• D
  None of these,None of these,+$4$,None of these