Final answer:
The suction temperature of an ammonia refrigeration system at 50° F corresponds to a pressure which can be found on an ammonia pressure-temperature chart, which is necessary to determine the correct psi value. Option A is correct.
Step-by-step explanation:
The suction temperature of an ammonia refrigeration system refers to the temperature at which ammonia gas is drawn into the compressor from the evaporator.
To find the equivalence of this temperature in pressure (psi), one would typically refer to an ammonia pressure-temperature chart. These charts provide the saturation pressure at different temperatures for ammonia. The chart would indicate the pressure that correlates with the given suction temperature of 50° F.
Without the chart, we cannot provide the exact pressure, but the possible answers provided suggest that the question expects knowledge of typical P-T values for ammonia. None of the provided answers can be verified as correct without the reference chart. To answer such questions accurately, one should have access to industry-standard refrigeration pressure-temperature charts or tools.