1 The informal word is 'sleep'; I'm not sure of the formal one, but someone will know. PPS - Got it: 'rheum' (/ru:m/) - less common than the related adjectives 'rheumy' and 'rheumatic'
2 Informal - 'snot'; formal - 'mucus'
3 'Wax' or 'ear-wax' - the 'ear-' part is often not necessary (because of the context - either verbal or visual)
4 Yes - though possibly a bit formal.
5 All except this one! "Are these questions properly structured?" - though I think you may be interested in things other than structure. Perhaps you could ask 'Have I made/Please correct [either or both of these] any mistakes [I've made] in this post'.
PS 'Dirt' isn't countable; say 'sorts/kinds of dirt' or (informally) '[sticky] stuff'.
- For Teachers