$A$ concave mirror gives an image three times as large as the object placed at a distance of $20 \ cm$ from it. For the image to be real,the focal length should be ...... $cm$.

Standard entropy of $X_2, Y_2$ and $XY_3$ are $60, 40$ and $50 \, J \, K^{-1} \, mol^{-1}$,respectively. For the reaction,$\frac{1}{2} X_2 + \frac{3}{2} Y_2 \to XY_3, \Delta H = -30 \, kJ$,to be at equilibrium,the temperature will be .....$K$.

If the line $y=2x+c$ is a tangent to the circle $x^2+y^2=5$,then a value of $c$ is

Who proposed the theory that "Cells arise only from the pre-existing cells"?

The formula of the product formed when sodium thiosulphate solution is added to silver bromide is:

$A$ clock which keeps correct time at $20^{\circ} C$,is subjected to $40^{\circ} C$. If the coefficient of linear expansion of the pendulum is $12 \times 10^{-6} /{ }^{\circ} C$,how much time will it gain or lose per day?