Final answer:
The most effective contraception method for preventing sexually transmitted infections is condoms. They offer dual protection against both pregnancy and STIs, unlike other methods like diaphragms or spermicides. So, the correct answer is option is 3.
Step-by-step explanation:
When teaching a client about contraception, the nurse would include condoms as the most effective method for preventing sexually transmitted infections (STIs). While barrier methods like diaphragms and cervical caps prevent sperm from entering the uterus, and methods such as spermicides use chemicals to kill sperm, only condoms offer the dual purpose of preventing both pregnancy and the spread of STIs.
A vasectomy is an effective means of sterilization for those seeking a permanent solution, but it does not prevent STIs.