The number of oxygen atoms bonded to one phosphorous atom in $P_4O_6$ is

In an experiment with $15$ observations on $x$,the following results were available: $\sum x^2 = 2830$ and $\sum x = 170$. One observation that was $20$ was found to be wrong and was replaced by the correct value $30$. Then the corrected variance is:

The shadow of a tower standing on a level ground is found to be $60 \ m$ longer when the Sun's altitude is $30^{\circ}$ than when it is $45^{\circ}$. The height of the tower is

During the electrolysis of cryolite,aluminium and fluorine are formed in ........ molar ratio :

Which of the following statements are correct?
$(i)$. Genus comprises a group of related species.
$(ii)$. Taxon represents a taxonomic group of individual organisms.
$(iii)$. Family comprises a group of related genera.
$(iv)$. Taxonomic category class includes related orders.

The rate of formation of new organic matter by a rabbit in a grassland is called: