Which of the following statements is not true?

What is $Calgon$,used as a water softener?

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:

What is meant by 'demineralised' water and how can it be obtained?

Identify the statements which are not correct from the following:
a) In the structure of ice,each oxygen atom is surrounded by $4$ other hydrogen atoms via hydrogen bonding.
b) Temporary hardness of water is due to dissolved $Mg(HCO_3)_2$ and $Ca(HCO_3)_2$,not $NaHCO_3$.
c) In the reaction of acidified $KMnO_4$ and $H_2O_2$,$H_2O_2$ acts as a reducing agent.
d) $3 \ g \ L^{-1}$ $H_2O_2$ is not equal to $100$ volume $H_2O_2$ (since $100$ volume $H_2O_2$ is approximately $303.7 \ g \ L^{-1}$).

The charring of sugar takes place when treated with concentrated $H_2SO_4$. What is the type of reaction involved in it?