A sample of metal weights 210g in air, 180g in water and 120g in liquid. Then Relative Density(RD) of

RD of metal $\mathrm{I}=\frac{{\mathrm{W}}_{\text{air }}}{{\mathrm{W}}_{\text{air }}-{\mathrm{W}}_{\text{water }}}=\frac{210}{210-180}=7$
Loss of weight in liquid=up thrust in liquid $(210-120)=\left(\frac{210}{7}\right)\left(\mathrm{RD}\text{ of liquid }\right)$
$\therefore$Relative density of liquid = 3