Which biological molecule in living organisms contains $Mg$ as an essential component?

Optical activity is shown by

Identify the source of linen from the following:

Which of the following statements are correct?
a) In maltose,$C-1$ of one $\alpha-D$-glucose is linked to $C-4$ of second $\alpha-D$-glucose.
b) Quaternary structure of protein represents spatial arrangement of two or more polypeptide chains with respect to each other.
c) Nucleotide units in a nucleic acid are joined to each other through a phosphodiester linkage.
d) Abnormally low level of thyroxine leads to hypothyroidism.

Identify the correct statements from the following:
$I)$ When $DNA$ is hydrolysed,adenine and thymine are obtained in equal quantities.
$II)$ When $RNA$ is hydrolysed,adenine and uracil are obtained in equal quantities.
$III)$ Amylose is a branched polymer with $\alpha-1 \rightarrow 4$ and $\alpha-1 \rightarrow 6$ glycosidic linkages.
$IV)$ Addison disease is due to the abnormal functioning of adrenal cortex.

Which gas is eliminated in fermentation?