All answers begin with 'o'.
-1. A region with O becomes a vital layer of the atmosphere. 5 letters
-2. The second musical note with O makes a mineral, which can be extracted profitably. 3
-3. O and an exclamation of surprise makes an S-shaped moulding or curve. 4
-4. O and a coniferous tree starts expressing views. 5
-5. O with a preposition meaning position makes a delicious cereal. 3
-6. O and a creeper make the adjective form of sheep. 5
-7. A writing tool with O is never shut. 4
-8. Something empty with O becomes egg shaped. 5
9. O with you and I leaves us in debt. 3 (two possible answers)
-10. Variety with O becomes a colour or a fruit. 6