Choose the substance with the lowest vapor pressure at a given temperature. arco2cai2bf3pf5

c. CaI_2 calcium iodide.

Explanation:

It is a common rule that vapor pressure is inversely proportional to boiling point of the substance. That is larger the boiling point smaller will be the vapor pressure.

B.P. of Ar= -185.8 °C

B.P. of CO2= -78.46 °C

B.P. of calcium iodide= 1,100 °C

B.P. of BF3 = -100.3 °C

B.P. of PF5= −84.6 °C

clearly, Boiling point of calcium iodide is highest hence, its vapor pressure is least among all the options.