Which of the following is not a type of cancer?

Amongst $TiF_6^{2-}$,$CoF_6^{3-}$,$Cu_2Cl_2$ and $NiCl_4^{2-}$,the colourless species are:

If the equation of one tangent to the circle with centre at $(2, -1)$ from the origin is $3x + y = 0$,then the equation of the other tangent through the origin is

Half-life of a radioactive substance is $20 \ minutes$. The time between $20\%$ and $80\%$ decay will be ........... $minutes$.

$A$ body falling from a height of $10\,m$ rebounds from a hard floor. If it loses $20\%$ of its energy on impact,then the coefficient of restitution is:

The period of a simple pendulum, whose bob is a hollow metallic sphere, is $T$. The period is $T_1$ when the bob is filled with sand, $T_2$ when it is filled with mercury, and $T_3$ when it is half-filled with mercury. Which of the following is true?