Which of the following gases can displace all other gases from a mixture?

Which of the following pairs has both members from the same group of the periodic table?

With the help of the following reactions,arrange metals $A$,$B$,$D$,and $E$ in decreasing order of their reactivity:
$(I)$ $B + ANO_3 \to BNO_3 + A$
$(II)$ $A + HCl \to ACl + \frac{1}{2}H_2$
$(III)$ $D + ECl \to DCl + E$
$(IV)$ $D + HNO_3 \to H_2$ gas is not evolved

How does the chemical reactivity change as we move from left to right across a period in the periodic table?

Which of the following sets of elements have the strongest tendency to form anions?

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 $(F)$?