$n \ g$ of substance $X$ reacts with $m \ g$ of substance $Y$ to form $p \ g$ of substance $R$ and $q \ g$ of substance $S$. This reaction can be represented as,$X + Y \rightarrow R + S$. The relation which can be established in the amounts of the reactants and the products will be

• A
  $n - m = p - q$
• B
  $n + m = p + q$
• C
  $n = m$
• D
  $p = q$