Which component of a lichen is heterotrophic?

$300 \, g$ of water at $25^{\circ} C$ is added to $100 \, g$ of ice at $0^{\circ} C$. The final temperature of the mixture is ........... $^{\circ} C$.

White vitriol is:

Two beams of light having intensities $I$ and $4I$ interfere to produce a fringe pattern on a screen. The phase difference between the beams is $\pi/2$ at point $A$ and $\pi$ at point $B$. Then the difference between the resultant intensities at $A$ and $B$ is (in $I$)

Who first discovered protoplast fusion?

Which of the following pairs contains structurally similar substances?