X and Y are elements. Two chemical species X and Y combine together to form a product P which contains both X and Y.       

                                           $X+Y\to P$

X and Y cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning species X, Y, and P are correct?

(i) P is a compound.

(ii) X and Y are compounds.

(iii) X and Y are elements.

(iv) P has a fixed composition.

The reaction of the burning of carbon in oxygen is represented by equation

$\mathrm{C}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \stackrel{}{\to } {\mathrm{CO}}_2\left(\mathrm{g}\right)+\mathrm{Heat}+\mathrm{Light}$

When 9.0 g of solid carbon is burnt in 16.0 g of oxygen gas the mass of carbon dioxide gas formed would be:

(Note: Atomic mass of C-12,o u, O=16.0 u)

Select from the following figure(s) that correctly represent(s) the experimental set-up for the verification of conservation of mass in a chemical reaction.
${\mathrm{BaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{BaSO}}_4\left(\mathrm{s}\right)+2\mathrm{NaCl}\left(\mathrm{aq}\right)$

The law of constant proportion was stated by Proust as?