Which of the following secretes interferons?

The voltage of an $ac$ source varies with time according to the equation $V = 100 \sin(100 \pi t) \cos(100 \pi t)$,where $t$ is in seconds and $V$ is in volts. Then:

The number of geometrical isomers for octahedral $[Co(NH_3)_2Cl_4]^-$,square planar $[AuCl_2Br_2]^-$ and $[Pt(en)Cl_2]$ are

Which of the following will not show geometrical isomerism?

If $f(x) = \sqrt{\frac{x - \sin x}{x + \cos^2 x}}$,then $\lim_{x \to \infty} f(x)$ is

Lithium metal crystallises in a body-centred cubic $(BCC)$ crystal. If the length of the side of the unit cell of lithium is $351 \ pm$,the atomic radius of the lithium will be ............. $pm$.