Hey there! So by definition, chiral centers have 4 different substituents so following the definition, the central carbon in the first 2 examples are not chiral centers. But they would be stereogenic centers since changing the position of OH will yield a different stereoisomer. Let's get to the last problem first. So always remember at this level in orgo, "alcohol beats all". This only means that you would prioritize alcohol in numbering. The way you wrote the name is already right except for the numbers. You did right in listing the halogens alphabetically. For the first 2 problems, as I've said earlier, the middle carbon is a stereogenic center so you would have to assign r for the first one and s for the second. Also, for multiple OH, you will use prefixes such as tri- in this case for 3 OH, and di- for 2 OH. The names and structures are shown below.