C.

Blue

Resolving Power or resolution is the ability of the lens to distinguish fine details and structure. It is the ability of a lens to differentiate between two points at a specified distance apart. 

Resolving Power =$\frac{\mathrm{Wavelength} \mathrm{of} \mathrm{light}}{2 \times \mathrm{NA}}$

It depends upon 2 factors:

(i) Wavelength of light used for illumination

(ii) Power of objective lenses

Among Yellow, green, red and blue light; Blue colour has the shortest wavelength so, it will give best resolution.

A.

20 mm Hg

Kidneys help in the formation of urine, from the blood flowing through glomerular capillaries. About 20% of plasma fluid filters out into the Bowman's capsule through a thin glomeular- capsular membrane due to a net or effective filtration of about 10 to 15 mm Hg.

D.

movement of chromosomes towards poles

Chromosomes are responsible for the transmission of the hereditary information from one generation to the next. Arms of the chromosome is known as chromatid. They are joined together in the centre known as centromere or primary constriction. During cell division, spindle fibres attach to centromere and help in the movement towards the poles.

D.

loss of cell mediated immunity

Thymus gland is located in the upper part of thorax near the heart. It is a bilobed, pinkish gland. It secretes thymosin hormone, thymic humoral factor and thymopoietin. 

Proliferation of lymphocytes and differentiation of these lymphocytes into a variety of clones are induced by these factors. These clones are differentially specialized to destroy different specific category  of antigens and pathogens. Therefore, thymus gland brings fourth T- lymphocytes for cell mediated immunity.

D.

leucocytes

G-6-P dehydrogenase deficiency is associated with haemolysis of RBCs.