Option 1: An embryo. This option is incorrect. The coconut water from a tender coconut is not the embryo of the coconut. The embryo is the part of the coconut that develops into a new coconut plant.

Option 2: A free nuclear endosperm with multiple nuclei. This option is correct. The coconut water in a tender coconut is the liquid endosperm of the coconut. Endosperm is the nutritive tissue that surrounds the embryo in the seed. In the case of the coconut, the endosperm is liquid and contains multiple nuclei.

Option 3: A cellular endosperm. This option is incorrect. The coconut water is not cellular in nature. It is a liquid endosperm without distinct cell structures.

Option 4: A non-nutritive fluid. This option is incorrect. The coconut water in a tender coconut is indeed a nutritive fluid. It contains various important nutrients such as sugars, electrolytes, vitamins, and minerals.

In conclusion, option 2 is the correct answer as the coconut water from a tender coconut is a free nuclear endosperm with multiple nuclei.