Which of the following metals will not reduce $H_2O$?

If $x^2+y^2=t+\frac{1}{t}$ and $x^4+y^4=t^2+\frac{1}{t^2}$, then $x^3 y \frac{d y}{d x}$ is equal to

The equation of a curve in polar coordinates is $\frac{l}{r} = 2 \sin^2 \frac{\theta}{2}$. This equation represents:

Yeast is used in the production of

The set of solutions of the system of equations
$
\begin{aligned}
x+y & =\frac{2 \pi}{3} \\
\text{and} \quad \cos x+\cos y & =\frac{3}{2},
\end{aligned}
$
where $x, y$ are real,is

During the change of $O_2$ to $O_2^-$,the incoming electron goes to the orbital