Castor oil is obtained from which of the following plants?

Two thin lenses of focal lengths $f_1$ and $f_2$ are in contact and coaxial. The power of the combination is

When a certain circuit consisting of a constant $e.m.f.$ $E$, an inductance $L$, and a resistance $R$ is closed, the current in it increases with time according to curve $1$. After one parameter $(E, L, \text{or } R)$ is changed, the increase in current follows curve $2$ when the circuit is closed a second time. Which parameter was changed and in what direction?

The correct order of second $I.E.$ of $C, N, O$ and $F$ is:

$C_2H_6 \stackrel{450^{\circ}C}{\longrightarrow} C_2H_4 + H_2$. The above reaction is called:

$A$ steel meter scale is to be ruled so that millimeter intervals are accurate within about $5 \times 10^{-5} \ m$ at a certain temperature. The maximum temperature variation allowable during the ruling is (Coefficient of linear expansion of steel $= 10 \times 10^{-6} \ K^{-1}$) (in $^{\circ} C$)