The tiger is left with 10J of energy in a grass–deer–tiger food chain. The energy available at grass level is: 

1000 J

The correct answer is Option (3) - 1000 J

To explain how much energy was available at the grass level, let's use the 10% rule of energy transfer in trophic levels:

Energy Transfer Efficiency: According to the 10% rule, only about 10% of the energy from one trophic level is transferred to the next. The remaining 90% is lost mainly through metabolic processes and heat.

Energy Calculation: Given that the tiger retains 10J of energy, let's backtrack through the trophic levels to determine the energy available at the grass level.

• Tertiary Consumer (Tiger): 10J
• Secondary Consumer (Deer): Since only 10% of the deer's energy is transferred to the tiger, the deer must have had 10J × 10=100 J
• Primary Consumer (Deer): 100J
• Primary Producer (Grass): Since only 10% of the grass's energy is transferred to the deer, the grass must have had 100J × 10=1000J

 Therefore, the energy available at the grass level is 1000J.