Answer:50 units of energy are available to the first-level consumers.
Step-by-step explanation:
TERTIARY CONSUMERS 0.5
SECONDARY CONSUMERS 5
PRIMARY CONSUMERS 50
PRODUCERS 500
Every unit of energy available at the producer level decreases on every level raised. The unit of energy goes down by 10% in every level. Thus, when the energy from producers, 500 units, goes up to the first-level consumer or primary level, it energy becomes 50.