"Hydrogen sulphide gas burns in air to given water and sulphur dioxide". The balanced equation for this reaction is 

Some compounds along with their chemical formulae are given below.

On the basis of formulae given above, the valencies or charges on ions are given below. Select the incorrect option.

Consider the following reaction,

X calcium carbonate + Y phosphoric acid $\to$ Calcium phosphate + X water + X carbon dioxide.

What is the value of X and Y?

Consider the following statements.

I. A chemical equation tells us about the substances involved in a reaction.

II. It gives information about the symbols and formula of substances involved in a reaction.

III. It tells us about the atoms or molecules of the reactants and products involved in a reaction.

The correct statement(s) is/are

Consider the following equations.

$\mathrm{Pb}\left({\mathrm{NO}}_3{)}_2\right(\mathrm{aq}) +2\mathrm{KI} (\mathrm{aq}) \to {\mathrm{Pbl}}_2(\mathrm{w}) +2{\mathrm{KNO}}_3$(x)

$\mathrm{Zn}\left(\mathrm{y}\right) +{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right) \to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right) +{\mathrm{H}}_2\left(\mathrm{z}\right)$

What are w, x, y and z in the above equations?