Which of the following is basic in nature?

The disease known as fluorosis is caused by the reaction of excess fluorine in the body with which of the following?

Which of the following has the highest value of cohesive energy?

$A$ chloride is soluble in cold water. When it is placed on a $Pt$ wire and heated in a Bunsen flame,it does not impart any characteristic color to the flame. Which of the following cations is present?

The frequency of the radiation emitted by alkali metals in the flame test follows the order:

$A$ substance $X$ is a compound of an element of group $IA$. The substance $X$ gives a violet colour in flame test. $X$ is