If the power of two lenses and $P_1$ and $P_2$; when they are combined; the effective power is:

0.1 M NaCl and 0.1 M CH₃COOH are kept in separate containers. If their osmotic pressures Are P₁ and P₂ respectively then the correct statement is:

The atmospheric pressure at earth surface is $P_1$ and inside a mine is $P_2$. They are related as :
(a) $P_1=P_2$

(b) $P_1>P_2$
(c) $P_1<P_2$

(d) $P_2=0$

V verus T curves at constant pressures $P_1$ and $P_2$ for an idealgas are shown in the figure,

The pressure $P_1$ at a certain depth in river water and $P_2$ at the same depth in sea water are related as: