What is the product formed when salicylic acid is reacted with zinc dust?

The diode used in the circuit shown in the figure has a constant voltage drop of $0.5 \, V$ at all currents and a maximum power rating of $100 \, mW$. What should be the value of the resistor $R$,connected in series with the diode,to obtain the maximum current?

Sulphuric acid reacts with $PCl_5$ to give

From which of the following is quinine obtained?

The silicate having one monovalent corner oxygen atom in each tetrahedron unit is:

$A$ uniform but time-varying magnetic field $B(t)$ exists in a circular region of radius $a$ and is directed into the plane of the paper,as shown. The magnitude of the induced electric field at point $P$ at a distance $r > a$ from the centre of the circular region is: