If the earth were to suddenly contract to $\frac{1}{n}^{th}$ of its present radius without any change in its mass,then the duration of the new day will be:

Secondary sewage treatment is mainly a

For the energy levels in an atom,which of the following statements is(are) correct?

If the circle $x^2+y^2+8x-4y+c=0$ touches the circle $x^2+y^2+2x+4y-11=0$ externally and cuts the circle $x^2+y^2-6x+8y+k=0$ orthogonally,then $k=$

Two circular coils $X$ and $Y$,having an equal number of turns,carry equal currents in the same sense and subtend the same solid angle at point $O$. If the smaller coil $X$ is midway between $O$ and $Y$,and if we represent the magnetic induction due to the bigger coil $Y$ at $O$ as $B_Y$ and that due to the smaller coil $X$ at $O$ as $B_X$,then $\frac{B_Y}{B_X}$ is

$A$ compound $X$ upon reaction with $H_{2}O$ produces a colorless gas $Y$ with a rotten fish smell. Gas $Y$ is absorbed in a solution of $CuSO_{4}$ to give $Cu_{3}P_{2}$ as one of the products. Predict the compound $X$.