Final answer:
The resulting pressure of a monatomic ideal gas when it is compressed isothermally to one-third of its initial volume will be three times as large as the initial value.
Step-by-step explanation:
The question is asking about the behavior of a monatomic ideal gas during an isothermal compression. When a monatomic ideal gas is compressed isothermally (meaning the temperature remains constant) to one-third of its initial volume, Boyle's Law applies, which states that the pressure of a given mass of an ideal gas is inversely proportional to its volume when the temperature is kept constant (P1V1 = P2V2). Thus, if the volume is reduced to one-third, the pressure will increase to three times its initial value, since P1V1 = P2V2 implies (P1)(V1) = (P2)(1/3V1), and hence P2 = 3P1.