If $\cos ^{-1}\left(\frac{x}{2}\right)+\cos ^{-1}\left(\frac{y}{3}\right)=\theta$,then $9x^2-12xy\cos \theta+4y^2=$

Leaching of $Ag_2S$ is carried out by heating it with a dilute solution of

The total number of nitrogenous bases in the human genome is estimated to be about

Among $TiF_6^{2-}, CoF_6^{3-}, Cu_2Cl_2$ and $NiCl_4^{2-}$,the colourless species are:

Which of the following statements are correct?
$(i)$ In prokaryotic cells,a special membranous structure formed by the extension of the plasma membrane into the cell is known as polysome.
$(ii)$ The smooth endoplasmic reticulum is the major site for synthesis of glycoproteins.
$(iii)$ $RuBisCO$ is the most abundant protein in the whole biosphere.
$(iv)$ Mitochondria,chloroplasts and peroxisomes are not considered as part of endomembrane system.
Of the above statements:

In a standing wave on a string rigidly fixed at both ends: