The coefficient of $x^4$ in the expansion of $\frac{(1-3x)^2}{(1-2x)}$ is equal to

$A$ gaseous mixture contains $50\%$ helium and $50\%$ methane by volume. What is the percentage of methane by weight in the mixture?

$A$ uniform cube is subjected to volume compression. If each side is decreased by $1\%,$ then the bulk strain is

An oil drop having a mass $4.8 \times 10^{-13} ~kg$ and charge $2.4 \times 10^{-18} ~C$ stands still between two charged horizontal plates separated by a distance of $1 ~cm$. If now the polarity of the plates is changed,the instantaneous acceleration of the drop is: $(g = 10 ~ms^{-2})$ (in $~ms^{-2}$)

Which of the following supports a dense population of plankton and littoral vegetation?

Which of the following compounds is formed by the addition of a mineral acid to an aqueous solution of borax?