The existence of a substance in more than one solid modification is known as:

The number of photo-electrons emitted per second from a metal surface increases when

Consider the set of all triangles $OPQ$ where $O$ is the origin and $P$,$Q$ are distinct points in the plane with non-negative integral coordinates $(x, y)$ such that $5x + y = 99$. The number of such distinct triangles whose area is a positive integer is:

If $\int \sec ^2 x \operatorname{cosec}^4 x \, dx = -\frac{1}{3} \cot ^3 x + k \tan x - 2 \cot x + C$, then $k$ is equal to

The longest phase of meiosis is:

Which of the following carbides will give propyne on hydrolysis?