………. is a semipermeable membrane.
A. Copper ferrocyanide
B. Copper ferricyanide
C. Copper Sulphate
D. Potassium ferrocyanide

Hint: Semipermeable membranes are a type of Biological, synthetic or polymeric membranes which have an inherent nature to allow only certain type of ions or molecules to pass through them via the process of osmosis or in some cases via facilitated diffusion and active or passive transport.

Complete step-by-step answer:There are various type of semipermeable membranes used in laboratories and also present in our body some of them are:
i.Cation exchange membrane (CEM)
ii.Charge mosaic membrane (CMM)
iii.Bipolar membrane (BPM)
iv.Anion exchange membrane (AEM)
v.Alkaline anion exchange membrane(AAEM)
vi.Proton exchange membrane.
To act as a semipermeable membrane of any of the above type the primary requirement is a gelatinous structure which is not just found in cases of Copper ferricyanide, Copper sulphate, Potassium ferrocyanide and thus the only viable solution is option A. Copper ferrocyanide.

Additional Information: A famous application of Copper ferrocyanide as a semipermeable membrane is in Berkley Hartley method which is a famous method for deduction of osmotic pressure in laboratories across the world.
Osmotic pressure is the pressure that must be applied on a more concentrated solution connected to a pure solvent via a semipermeable membrane so as to prevent flow of pure solvent towards it due to osmosis through a semipermeable membrane.

Note:The compound Copper ferrocyanide is pretty famous for being used in the Betley Hartley process as a semipermeable membrane thus you must keep its name in mind as in these types of questions memory of an answer is the only way out to solve it.