This sentence states that Mr. Kops has been involved in the PTA for a decade! He's been involved with the events at his kid's school, so he seems to be the best one to support. The statement makes it seem like he knows what is going on in the schoo. This statement seems to be the most credible.
A prefix is a part of a etymology that modifies are word at the start of it: i.e. reconsider, involuntary, uncover.
A suffix is the same thing but it modifies the end of a word: i.e. walked, bigger, reversible.
De is a prefix meaning "down, away" or "denoting removal or reversal". In this case it is referring to demagnetizing something, or removing the magnetization.
Ize is a suffix meaning to "make or become". This is referring to an object becoming magnetized.
