Why are antiparallel beta sheets more stable than parallel beta sheets?

Which item is most likely part of the safety contract

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

Achemist reacted 57.50 grams of sodium metal with an excess amount of chlorine gas. the chemical reaction that occurred is shown. na + cl2 → nacl if the percentage yield of the reaction is 86%, what is the actual yield? show your work, including the use of stoichiometric calculations and conversion factors.