Which of the following elements does not show allotropy?

The length of the transverse common tangent of the circles $x^2+y^2-2x+4y+4=0$ and $x^2+y^2+4x-2y+1=0$ is

The lanthanide contraction is responsible for the fact that

Which element is common in both hemoglobin and myoglobin?

When an orange solution containing $Cr_2O_7^{2-}$ ions is treated with an alkali,a yellow solution is formed,and when $H^{+}$ ions are added to the yellow solution,an orange solution is obtained. Explain why this happens.

An air bubble of radius $1 \ cm$ rises from the bottom portion through a liquid of density $1.5 \ g/cc$ at a constant speed of $0.25 \ cm/s$. If the density of air is neglected,the coefficient of viscosity of the liquid is approximately,(in $Pa \cdot s$):