Which substance is used as a smoke screen in warfare?

Teak wood is obtained from which plant?

$A$ body projected vertically upwards crosses a point twice in its journey at a height $h$ just after $t_1$ and $t_2$ seconds. Maximum height reached by the body is

$A$ student is allowed to select at most $n$ books from a collection of $(2n + 1)$ books. If the number of ways to select at least one book is $63$,then the value of $n$ is:

$A$ lead shot of $1\, mm$ diameter falls through a long column of glycerine. The variation of its velocity $v$ with distance covered is represented by

Who first discovered lichens?