If the roots of the equations $px^2 + 2qx + r = 0$ and $qx^2 - 2\sqrt{pr}x + q = 0$ are real,then

$A$ and $B$ are two radioactive substances whose half-lives are $1$ and $2$ years respectively. Initially, $10 \, g$ of $A$ and $1 \, g$ of $B$ are taken. The time (approximate) after which they will have the same quantity remaining is ........... $years$.

If $\overrightarrow{a} = 2\widehat{i} - \widehat{j} + \widehat{k}$,$\overrightarrow{b} = \widehat{i} + \widehat{j} - 2\widehat{k}$ and $\overrightarrow{c} = \widehat{i} + 3\widehat{j} - (\lambda^2 + 3\lambda)\widehat{k}$ (where $\lambda$ is a constant) and $\overrightarrow{a}$ is perpendicular to $\overrightarrow{c} - \lambda\overrightarrow{b}$,then the sum of different values of $\lambda$ is:

What is a species?

The ratio of angular speeds of the minute hand and the hour hand of a watch is

With respect to chlorobenzene,which of the following statements is not correct?