For nh4+, write an equation that shows how the cation acts as an acid
for co3+, write an equation that shows how the cation acts as an acid.
for ch2nh3+, write an equation that shows how the cation acts as an acid.

Cations and anions are fancy words for positive and negative ions respectively. I like to remember it by saying to myself 'which electrode would it be attracted to?'. A positively charged ion would move towards the negatively charged cathode, hence 'cation', and the reverse is true for 'anion'.

Okay, by the Bronsted-Lowry theory of acids and bases, an acid is a species that donates a proton and a base is a species that accepts a proton. Given that a proton is simply a H+ cation, any substance containing a hydrogen atom has the capacity to behave as an acid. The first answer is:

NH4+ --> NH3 + H+

CO3+ cannot by itself act as an acid, for the simple reason that it does not contain any hydrogen atoms. Hence this seems to be a trick question!

CH2NH3+ will most likely lose a proton from the positively charged NH3 part of the molecule, so as to neutralise the charge of the organic molecule:

CH2NH3+ --> CH2NH2 + H+

I hope this helps you :)