$A$ pendulum suspended from the ceiling of a train oscillates with a time period $2\,s$,when the train is accelerating at $10\,m/s^2$. What will be its time period when the train retards at $10\,m/s^2$?

Which one of the following is the first step in taxonomy?

Given below are $2$ statements:
Statement $I$: The number of species among $BF_4^-$,$SiF_4$,$XeF_4$ and $SF_4$,that have unequal $E-F$ bond lengths is $2$. Here,$E$ is the central atom.
Statement $II$: Among $O_2^-$,$O_2^{2-}$,$F_2$ and $O_2^+$,$O_2^-$ has the highest bond order.
In the light of the above statements,choose the correct answer from the options given below

Product $(A)$ is

If the slope of one of the lines in the pair of lines $8x^2 + axy + y^2 = 0$ is thrice the slope of the other line,then $a =$

Fungi are filamentous with the exception of $X$ which is unicellular. Identify $X$.