If someone in chemistry could me with this with explanation

1.)read the following statements. which ones are correct? be sure to explain how you know.

bf3 and pf5 are examples of violations of the octet rule.
bf4− and bf3-nh3 are examples of violations of the octet rule.
expanded valence shells occur most often when the central atom is bonded to a small, electronegative element.
the central atoms most capable of having expanded valence shells come from rows 3, 4, and 5 of the periodic table.

2.)what is the steric number and the bond angles associated with each of the following molecules if a is the central atom, x refers to the atoms bonded to it and there are no lone pairs on the central atom.

ax3
ax4
ax6

The answer to your question really depends on three things: how much water you have, how cold it is to start out, and how cold the things around it are. water actually freezes when it gets to 32 degrees fahrenheit (0 degrees celsius), but the time it takes to get there may be different.  let's start with the first. if you take two glasses, and fill one with a tiny bit of water, and the other about halfway, then put them both in the freezer, the one with less water will freeze first (you can try this at home, but i recommend using plastic cups and not glass ones).  now let's move on to the second part. let's say you have two glasses, and you fill one with really cold water that has been in the refrigerator, and the other with really hot water from the sink. if you put both of them in the freezer, the one that started out colder will freeze first.  for the third part, let's imagine that you have two glasses with the same amount of water in them, and the water is at the same temperature. imagine putting one outside on a really really cold day in georgia, and having a friend in alaska put one outside on the same day. since it would be so much colder in alaska, the glass of water there would freeze before yours.  so, if you took a tiny bit of really cold water in a glass, and put it outside on a cold day in alaska, it would freeze a lot faster than a big glass of hot water outside on a cold day in georgia. 

I'm sorry but i'm only grade

Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.