Which of the following is the best scientific method to test the presence of water in a liquid?

Which salt does not cause hardness in water?

Polyphosphates are used as water softening agents because:

Which of the following is not correct for $D_2O$?

An inorganic salt $(A)$ is decomposed on heating to give two products $(B)$ and $(C)$. Compound $(C)$ is a liquid at room temperature and is neutral to litmus,while the compound $(B)$ is a colourless neutral gas. Compounds $(A)$,$(B)$ and $(C)$ are:

Identify the reactions in which $H_2O$ is oxidised:
$I$. Photosynthesis
$II$. Reaction of $H_2O$ with fluorine
$III$. Reaction of $H_2O$ with hydrogen
$IV$. Reaction of $H_2O$ with $P_4O_{10}$
The correct answer is