In known elements,the maximum number is of

The electronic configurations of four elements are:
$I.$ $[Kr]\, 5s^1$
$II.$ $[Rn]\, 5f^{14}\, 6d^1\, 7s^2$
$III.$ $[Ar]\, 3d^{10}\, 4s^2\, 4p^5$
$IV.$ $[Ar]\, 3d^6\, 4s^2$
Consider the following statements:
$(i)$ $I$ shows variable oxidation state
$(ii)$ $II$ is a $d$-block element
$(iii)$ The compound formed between $I$ and $III$ is covalent
$(iv)$ $IV$ shows single oxidation state
Which statement is True $(T)$ or False $(F)$?

Arrange the following in the order of increasing basic character: $(NO_2, K_2O, ZnO)$

Which of the following represents the correct order of acidic strength?

The oxide of a metal $(R)$ can be reduced by the metal $(P)$,and metal $(R)$ can reduce the oxide of metal $(Q)$. Then the decreasing order of the reactivity of metals $(P)$,$(Q)$,and $(R)$ with oxygen is:

The reactivity of the following compounds toward water is in the order: