**Core Concept**
The ESI (Employees' State Insurance) Act provides maternity benefits to insured women, ensuring their financial security and well-being during pregnancy, childbirth, and post-natal care. This legislation aims to reduce the economic burden on women and encourage them to seek medical care during these critical periods.

**Why the Correct Answer is Right**
The duration of maternal benefit under the ESI Act is 26 weeks, which includes 12 weeks of maternity leave and 26 weeks of extended maternity benefit. This extended benefit period allows women to recover from childbirth, care for their newborn, and return to work when they are fully recovered. The ESI Act also mandates that employers maintain the woman's job and seniority during this period.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the duration of maternal benefits under the ESI Act.
**Option B:** This option is incorrect because it is too short and does not account for the extended benefit period.
**Option C:** This option is incorrect because it is too long and exceeds the maximum duration of maternity benefits under the ESI Act.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the ESI Act also provides medical benefits to insured women, including prenatal care, delivery expenses, and post-natal care, ensuring their overall health and well-being.

**Correct Answer:** C. 26 weeks.