[单选题]
A monatomic gas is cooledp/(+ay0jrgo wff4 be6 b6hg+ ; sl psjb *n306pio9cjfwy 50 K at constant volume when 831 J of energy is removed from it. Hcpsp 0b+l;i96h6gnjs w*o 3jf ow many moles of gas are in the sample?
A. $2.50 \; mol$
B. $1.50 \; mol$
C. $1.33 \; mol$
D. none of the above
