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

RD of metal $=\frac{{\mathrm{W}}_{\text{air }}}{{\mathrm{W}}_{\mathrm{air}}-{\mathrm{W}}_{\text{water }}}=\frac{210}{210-180}=7$

Loss of weight in liquid=upthrust in liquid

$\therefore (210-120)=\left(\frac{210}{7}\right)\left(\mathrm{RD}\text{ of liquid }\right)$

$\therefore$  Relative density of liquid = 3