Как определить валентность у хлора!
И вообще как она определяется у других элементов?

Во дворе  ПОСЛИСЬ КУРЫ И КОЗЛЯТА. Козлят было в 3 раза менше чем кур. У  кур и козлят ног было 40. Сколько водворе козлят и кур было?

вставить глаголы в нужной форме: 
Melanie Stewart (say) that young teens (experiment) with alcohol for a variety of reasons. 
She (explain) that some teens (start) because they (associate) drinking with adulthood. 
Some teenagers (tell) her that the more teachers and parents (warn) them not to drink the more eager they (be) to try it. 
She (add) that probably the most powerful influence on young teens (be) their mates. 
She (say) that curiosity (may be) the most frequent motive for drinking alcohol. 
She also (mention) that teenagers (complain) about stress at school. 
She (agree) that schools (must be) the most important source on information on the dangers of alcohol.