AS aqa chem help please asap

so ive been doing a lot of questions and there are a lot of questions like
"State how krypton is ionised in the mass spectrometer" and the mark scheme is specific about either electrospray or electron impact but how am i supposed to know which type of ionisation it would be?

Electrospray ionisation is typically used for larger molecules, whereas small molecules and atoms can often be ionised with electron impact.

See here: https://filestore.aqa.org.uk/resources/chemistry/AQA-7404-7405-SG-TOFMS.PDF

oh okay! thank you - but for my example above i thought krypton was a small molecule but the mark scheme says it was ionised via electrospray?

Interesting. It is monatomic, but being a noble gas, removing an electron is probably pretty difficult given the first ionisation energies of the noble gases are pretty high.

It’s not immediately obvious imo and I think the MS should have been a little more lenient.

Interesting. It is monatomic, but being a noble gas, removing an electron is probably pretty difficult given the first ionisation energies of the noble gases are pretty high.

It’s not immediately obvious imo and I think the MS should have been a little more lenient.

wait i think it depends on the Mr, i found this on chemrevise "Electron impact is used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment."
ig Kr has a relatively high Mr so thats why its supposed to be electrospray ionisation