Astopwatch is calibrated for a time interval of 1/100th of a second with a range of 9 hours 59 minutes and 59.99 seconds. it also has a ± 5-seconds-a-day bias. this means this watch could gain or lose up to 5 seconds each day of use.

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e