The correct answer is option ($3$) as

Vault is a barrier method of contraception which is made of rubber that is inserted into the female reproductive tract to cover the cervix during the coitus.

– Option ($1$) is incorrect as periodic abstinence is also a natural method of contraception in which couples avoid coitus during the fertile period.

– Option ($2$) is incorrect as lactational amenorrhea is also a natural method of contraception which is based on the fact that ovulation and therefore the cycle do not occur during the period of intense lactational following parturition.

– Option ($4$) is incorrect as coitus interruptus is a natural method of contraception in which male partner withdraws his penis from the vagina just before ejaculation so as to avoid insemination.