Option 1 states that temperatures differing by 25° on the Fahrenheit (F) scale must differ by 45° on the Celsius (C) scale. This statement is incorrect. The correct conversion formula between Fahrenheit and Celsius is that every 1°F of difference corresponds to 5/9°C of difference. So, a difference of 25°F on the Fahrenheit scale would correspond to a difference of (5/9 * 25)°C on the Celsius scale, which is approximately 13.89°C, not 45°C.

Option 2 states that 0°F corresponds to -32°C. This statement is correct. 0°F is the freezing point of water on the Fahrenheit scale, and -32°C is the freezing point of water on the Celsius scale. These two temperatures are equivalent.

Option 3, which is the correct answer, states that temperatures which differ by 10° on the Celsius scale must differ by 18° on the Fahrenheit scale. This statement is correct. The conversion formula between Celsius and Fahrenheit is that every 1°C of difference corresponds to 9/5°F of difference. So, a difference of 10°C on the Celsius scale would correspond to a difference of (9/5 * 10)°F