Yes, "negotiable" is spelled correctly.
The word nite is more correctly spelled night.
You spelled it correctly!
You have spelled 'still' correctly.
Yes, engineer is spelled correctly in your question.
Flattest is spelled correctly. The others are spelled: silliest, biggest and sweetest.
Yes, surprisingly is spelled with an S. Surprisingly is how you spell it. You spelled it correctly.
You spelled it correctly the first time: exclamatory
You've spelled it correctly.
Convenience (easy access or availability) is correctly spelled.
Yes, "volunteer" is spelled correctly.
No, "infrachrondal" is not spelled correctly. The correct spelling is "infrachondral."