Salad (lettuce, tomato, and onion) a pure substance or a mixture ?

Iwould appreciate if someone could me.

Before it was launched, a helium-filled balloon had a pressure of 201 kpa at a temperature of 27°c. at an altitude of 15,000 m, the pressure had decreased to 2.5 kpa and the temperature had dropped to -14 °c. the volume of the balloon increased to 59.3 m3. what is the original volume of the balloon? 13 m3 0.85 m3 0.077 m3 1.17 m3

Which radioisotope is used to date fossils? a. oxygen-16 b. carbon-14 c. uranium-238 d. carbon-12