This flask originally held some copper wire and a clear solution of nitric acid. the two substances reacted and produced a brown gas and a blue solution. this reaction cannot be reversed. evidence of a chemical reaction is shown by a) ice forming. b) steam rising. c) the formation of a gas. d) a change in state from a solid to a liquid.

The correct answer is option (C).

Explanation:

Evidence which tells us that chemical reaction has occurred:

When the copper wire is held in clear solution of nitric acid brown colored gas was released with change in color of the solution. Both these observations means that chemical reaction has been taken place.

According to the option enlisted the correct answer is option (C).

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form