Explanation:

- Kanyadan: This is a ritual where the father gives away his daughter to the groom. Not legally obligatory under the Hindu Marriage Act but part of traditional Hindu weddings.

- Panigrahan: This translates to "holding the hand" and symbolizes acceptance. It is also not strictly required by law but is traditionally performed.

- Saptapadi: This involves taking seven steps around a sacred fire. Under the Hindu Marriage Act, it is considered essential. Marriage is not complete without these steps.

- All of the above: This suggests that all listed rituals are necessary under the Act, which is not the case.

Answer: Option 3 - Saptapadi is obligatory.