Significant figures chemistry

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

50 points! need answer asap. what type of organic compound contains the following functional group? (2 points)

Dumbledore decides to gives a surprise demonstration. he starts with a hydrate of na2co3 which has a mass of 4.31 g before heating. after he heats it he finds the mass of the anhydrous compound is found to be 3.22 g. he asks everyone in class to determine the integer x in the hydrate: na2co3·xh2o; you should do this also. round your answer to the nearest integ