Convenience (easy access or availability) is correctly spelled.
Yes it is spelled correctly
You have spelled 'still' correctly.
No word is always spelled correctly. But the word "correctly" is correctly spelled as correctly. (see related question)
Yes, surprisingly is spelled with an S. Surprisingly is how you spell it. You spelled it correctly.
Yes, you have spelled prosperous correctly.
You've spelled it correctly.
You spelled it correctly..
Yes, engineer is spelled correctly in your question.
Correctly: How did Elise spell? She spelled correctly.
You spelled it correctly in the question.
You've spelled it correctly.
You've spelled it correctly.