$解:(1) 设\rho ={\frac {k} {V}}$
$∵ 当V=10\ \mathrm {m^3}时,\rho =1.43\ \mathrm {kg/m^3}$
$∴ 1.43={\frac {k} {10}}$
$解得,k=14.3$
$∴ 函数表达式为\rho ={\frac {14.3} {V}}$
$(2) 当V=2\ \mathrm {m^3}时,\rho ={\frac {14.3} {2}}=7.15(\ \mathrm {kg/m^3})$
$∴ 当V=2\ \mathrm {m^3}时氧气的密度\rho为7.15\ \mathrm {kg/m^3}$