The velocity of a small ball of mass M and density d, when dropped in a container filled with glycerin becomes constant after some time. If the density of glycerin is $${d \over 2}$$, then the viscous force acting on the ball will be :

Column - I gives certain physical terms associated with flow of current through a metallic conductor. Column-II gives some mathematical relations involving electrical quantities. Match column-I and column-II with appropriate relations.

	Column - I		Column - II
(A)	Drift Velocity	(P)	$${m \over {n{e^2}p}}$$
(B)	Electrical Resistivity	(Q)	$$ne{\upsilon _d}$$
(C)	Relaxation Period	(R)	$${{eE} \over m}\tau $$
(D)	Current Density	(S)	$${E \over J}$$

Match Column - I and Column - II and choose the correct match from the given choices.

	Column - I		Column - II
(A)	Root mean square speed of gas molecules	(P)	$${1 \over 3}nm{\overline v ^2}$$
(B)	Pressure exerted by ideal gas	(Q)	$$\sqrt {{{3RT} \over M}} $$
(C)	Average kinetic energy of a molecule	(R)	$${5 \over 2}RT$$
(D)	Total internal energy of 1 mole of a diatomic gas	(S)	$${3 \over 2}{k_B}T$$

In the product

$$\overrightarrow F = q\left( {\overrightarrow v \times \overrightarrow B } \right)$$

$$ = q\overrightarrow v \times \left( {B\widehat i + B\widehat j + {B_0}\widehat k} \right)$$

For q = 1 and $$\overrightarrow v = 2\widehat i + 4\widehat j + 6\widehat k$$ and $$\overrightarrow F = 4\widehat i - 20\widehat j + 12\widehat k$$

What will be the complete expression for $$\overrightarrow B $$ ?