What r the chances of the male acquiring an STD if he isn't wearing a condom during oral sex?

Depends...... Good question but hard to answer. If engaging in sex with an ulcer or cut, definitely. Other factors includes the type of std, the "bug burden" in your partner performing oral sex , and other factors(eg duration, frequency).Otherwise, it is low probability.
Smalll chance. Oral sex is less but not zero in std risk. Oral flora can include stds such a herpes virus, etc.