Solid X is placed in contact with solid Y. Heat will flow spontaneously from X to Y when:
A. X is 10°C and Y is 5°C.
B. X is 20°C and Y is 20°C.
C. X is 25°C and Y is 30°C.
D. X is -25°C and Y is -10°C.
Heat flow is always from high temperature to low temperature. Watch out for negative numbers. In choice 4, Y is warmer than X and heat would flow from Y to X (not what the question asks).