Which of the following compounds has a negative enthalpy of solution?

Which of the following metals reacts directly with nitrogen to form a nitride?

Identify the correct statements from the following:
$A$) Among alkali metal ions,$Li^+$ has the highest hydration enthalpy.
$B$) The boiling point of alkali metals increases from $Li$ to $Cs$.
$C$) The density of $K$ is less than that of $Na$ and $Rb$.
$D$) $Li$ has a strong tendency to form superoxide.

Fluorosis disease is caused due to the reaction of ...... with excess of fluoride in the body.

Calcium is obtained by

Which pair of metals dissolves in $NaOH$ solution?