In which of the following reactions does hydrogen act as an oxidizing agent?

The number of proper subsets of the set ${1, 2, 3}$ is

$A$ tiny air bubble in a glass slab $(\mu = 1.5)$ appears from one side to be $6\, cm$ from the glass surface and from the other side,$4\, cm$. The thickness of the glass slab is......$cm$

If the roots of $x^3-42 x^2+336 x-512=0$ are in increasing geometric progression,then its common ratio is (in $: 1$)

In the Fraunhofer diffraction experiment,$L$ is the distance between the screen and the obstacle,$b$ is the size of the obstacle,and $\lambda$ is the wavelength of the incident light. The general condition for the applicability of Fraunhofer diffraction is:

Which of the following is not an example of a natural polymer?