How many atoms are present in a 

$(i)$ $H_2S$ molecule and

$(ii)$ $PO_4^{3-}$ ion ?

Calculate the number of molecules of sulphur $(S_8)$ present in $16 \,g$ of solid sulphur.

Write down the formulae of

$(i)$ sodium oxide

$(ii)$ aluminium chloride

$(iii)$ sodium suphide

$(iv)$ magnesium hydroxide

Convert into mole.

$(a)$ $12\, g$ of oxygen gas

$(b)$ $20\, g$ of water

$(c)$ $22\, g$ of carbon dioxide.

In a reaction, $5.3\, g$ of sodium carbonate reacted with $6\, g$ of acetic acid. The products were $2.2\, g$ of carbon dioxide, $0.9 \,g$ water and $8.2\, g$ of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.

sodium carbonate $+$ acetic acid $\to $ sodium acetate $+$ carbon dioxide $+$ water