Who discovered lichens?

$\frac{d}{d x} \sin ^{-1}\left(3 x-4 x^3\right)$ is equal to

$A$ current of $2\, A$ flows in a system of conductors as shown. The potential difference $(V_A - V_B)$ will be ................ $V$.

The number of $5$-digit numbers that are not divisible by $5$ and consist of different odd digits is:

Two radioactive nuclei $P$ and $Q$ in a given sample decay into a stable nucleus $R$. At time $t = 0$,the number of $P$ species is $4N_0$ and that of $Q$ is $N_0$. The half-life of $P$ is $1$ minute,while that of $Q$ is $2$ minutes. Initially,there are no nuclei of $R$ present in the sample. When the number of nuclei of $P$ and $Q$ are equal,the number of nuclei of $R$ present in the sample would be:

According to Robert May,the global species diversity is about ...................