The number of unpaired electrons in chromic ion $(Cr^{3+})$ is (atomic number of $Cr = 24$)

Which elements were identified by spectroscopy of their minerals?

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 $Cr(VI)$.

Which of the following rules must be followed to form an alloy?

Which of the following elements is not considered a transition element?

If $A$ is $[Rn]\,6d^2\,7s^2$,then identify the block,period,and group.