Choose the correct statement$(s)$.

What is meant by diagonal relationship?

$(a)$ $Be$ and $Mg$ are alkaline earth metals.
$(b)$ $K^{+}$ has larger radii than $Ca^{2+}$.
$(c)$ All $d$-block elements are transition elements.
$(d)$ $H^{-}$ ion is larger than $F^{-}$.
Incorrect statement is/are

Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However,oxygen has lower ionisation enthalpy than nitrogen. Explain.

$A, B$,and $C$ are hydroxy-compounds of the elements $X, Y$,and $Z$ respectively. $X, Y$,and $Z$ are in the same period of the periodic table. $A$ gives an aqueous solution of $pH < 7$. $B$ reacts with both strong acids and strong alkalis. $C$ gives an aqueous solution which is strongly alkaline.
Which of the following statements is / are true?
$I$: The three elements are metals.
$II$: The electronegativities decrease from $X$ to $Y$ to $Z$.
$III$: The atomic radius decreases in the order $X, Y$,and $Z$.
$IV$: $X, Y$,and $Z$ could be phosphorus,aluminium,and sodium respectively.

Which of the following orders is incorrect?