Which one can act as a semipermeable membrane?

During the phenomenon of osmosis,.....

The $pH$ of a $0.2 \ M$ aqueous solution of a dibasic acid $(H_2A)$ is $1.699$. Its osmotic pressure at $T \ K$ is ......... $RT$.

The size of a raw mango shrinks to a much smaller size when kept in a concentrated salt solution. Which one of the following processes can explain this?

At a constant temperature,the osmotic pressure of a solution is.....

What is a semi-permeable membrane? Give examples.