If the concentration of the stock solution is 25 m, what would be the dilution factor and concentration of sample 'c' with respect to original stock solution?

I won't be able to give an exact number because we are not given with the volume of the diluent and the aliquot. In order to explain this, I can give examples.

Dilution factor is the ratio of the initial volume and the final volume. For example, if you add 0.1 mL aliquot of the stock solution to 50 mL of the diluent like water, the dilution factor is:

Dilution Factor = Vi/Vf = 0.1 / (0.1+50) = 1/501

Consequently, the concentration of the sample is equal to the product of the concentration of the stock solution and the dilution factor:

Concentration of sample = 25 M * 1/501 = 0.05 M