Which of the following substances would quickly absorb oxygen?

The quantum number which explains the line spectra observed as doublets in the case of hydrogen and alkali metals and doublets and triplets in the case of alkaline earth metals is

The most appropriate magnetization $M$ versus magnetising field $H$ curve for a paramagnetic substance is

The ratio of the longest wavelengths corresponding to the Lyman and Balmer series in the hydrogen spectrum is

If the curves $y^2=6x$ and $9x^2+by^2=16$ intersect each other at right angles,then the value of $b$ is

Which of the following is the most stable ecosystem?