Which of the following contraceptive methods can be used by both males and females?

The chemical method of contraception includes:

An oral contraceptive pill checks:

$A$: Periodic abstinence is a natural method of contraception in which couples avoid or abstain from coitus from day $10$ to $17$ of the menstrual cycle,when ovulation is expected.
$R$: Day $10$ to day $17$ of the menstrual cycle is considered a safe period.

Which of the following methods of contraception has the maximum chances of failure?

Give scientific reasons: Pills taken orally prevent pregnancy.