If $a = \sqrt{21} - \sqrt{20}$ and $b = \sqrt{18} - \sqrt{17}$,then

If $y=\sin (\log _e x)$,then $x^2 \frac{d^2 y}{d x^2}+x \frac{d y}{d x}$ is equal to

The uncertainty in the location of a circulating electron is equal to its de-Broglie wavelength. The minimum percentage error in the measurement of its velocity under these circumstances will be approximately:

Opium is obtained from the latex of the unripe fruit of which plant?

Which of the following hydrides has the lowest boiling point?

The probability that a number selected at random from the set of numbers ${1, 2, 3, \ldots, 100}$ is a cube, is