A small section of a polymer chain, containing 10 repeating units, has a relative molecular mass of 625.
Which of the following monomers could have polymerised to form this chain?
ethylene
viyl chloride
styrene
glucose
If it's 10 units long then one unit must be 625/10 = 62.5.
Look up the four possibilities and see which has a molar mass of 62.5. For example, you know it can't be ethylene.
H2C=CH2 is 28. Glucose is C6H12O6 and that is 180 so it can't be that. You can finish.