In which of the following reactions does $H_2O_2$ act as a reducing agent?

If $(-2, 6)$ is the image of the point $(4, 2)$ with respect to the line $L = 0$,then $L$ is equal to

Parts $A, B, C$ and $D$ of the human eye are shown in the diagram. Select the option which gives correct identification along with its functions / characteristics:

Three rods $AB$,$BC$,and $BD$ made of the same material and having the same cross-section have been joined as shown in the figure. The ends $A$,$C$,and $D$ are held at temperatures of $20^{\circ}C$,$80^{\circ}C$,and $80^{\circ}C$ respectively. If each rod is of the same length,then the temperature at the junction $B$ of the three rods is: (in $^{\circ}C$)

In a standing wave on a string rigidly fixed at both ends:

$A$ wire fixed at the upper end stretches by length $l$ by applying a force $F$. The work done in stretching is