Which group of organisms was the first to exist on Earth among the given options?

In the Bohr series of lines of the hydrogen spectrum,the third line from the red end corresponds to which one of the following inter-orbit transitions in an atom of hydrogen?

$A$ $4 \mu F$ capacitor is charged by a $200 \ V$ battery. It is then disconnected from the supply and connected to another uncharged $2 \mu F$ capacitor. During the process,the loss of energy (in $J$) is:

For a reaction $\frac{1}{2} A \rightarrow 2B,$ the rate of disappearance of $A$ is related to the rate of appearance of $B$ by the expression:

Which of the following anions cannot be tested by dilute $H_2SO_4$?

$A$ point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at a distance of $9 \ m$ and $25 \ m$ respectively from the source. The ratio of the amplitudes of the waves at $P$ and $Q$ is