One still needs the information I alluded to previously. Without that, there is not enough information to answer the question without a lot of added provisos and qualifications. I guess what the examiner is trying to get at (and not very well, I suggest) is what effect a higher leaded fuel might have on an engine which proscribes the use of such fuel.
Silly question, methinks.
(a) did you have a read of the link I provided ?
(b) if the fuel is proscribed, then you don't go flying with it - having determined it is a bodgie spec, to do so would expose you to all sorts of potential consequences at the enquiry, so your answer needs to accommodate that consideration. Some more reading in the following monograph from the FAA
Engineering specialist in aircraft performance and weight control.
The question is vaguely worded, but I think what the examiner intended to say was that if your aircraft should be operating on 100LL fuel according to the flight manual or Pilot Operating Handbook, and you put a higher leaded fuel into the tanks, what is likely to happen.
A higher leaded fuel is likely to produce lead fouling of the cylinders and/or valve seats because the lower combustion temperatures of a lower compression engine allows the lead to settle as tiny beads of metallic lead contaminate the combustion chamber.