PLEASE HELP I DONT UNDERSTAND AT A

If the temperature of 153.7 L of a gas at 38.6 ºC falls by 9.6 Cº, what is the new volume of the gas if the pressure is constant?
Select one:
a. 149
b. 153.700
c. 115
d. 139.40

Which of the following is an indication that a substance has undergone a chemical change? a. no new product has been formed. b. the color of the substance has not changed. c. the original constitute has not changed. d. the molecular structure has changed.

Air can be considered a mixture. which statement does not explain why?

Molecular iodine, i2(g), dissociates into iodine atoms at 625 k with a first-order rate constant of 0.271 s−1. part a part complete what is the half-life for this reaction?