(Not a teacher)
These are my opinions, based on how the sentences sound to me:
In numbers 1 and 2, there isn't much difference grammatically or in meaning between the two choices. I would favor using the article in both. In 2, one could also say, "He alleged/alleges that (the) oil companies are engaged in manipulating the market to collect huge profits." If the reference is to oil companies in general, omit the article. If the reference is to a specific group of oil companies, use "the."
In number 3, if you leave the article off, "formation" may refer to the general or historical development of federations. But if today you are focusing on "the" formation of federations, the implication may be that you discussing the present or future formation of specific federations.
For number 4, Does "baptism of repentance" refer to a particular or special type of baptism or to a standard baptism in which one repents? If it is special, I would use the articles (choice "a"). If standard, the articles can be omitted but can be used as well.