Frost typically forms on the inside of a windowpane (rather than the outside) because:

The correct answer is: A. The inside of the pane is colder than the outside.

When the temperature outside is below freezing, the air inside your home can still be above freezing. As the warm, moist air from inside your home comes into contact with the cold windowpane, the water vapor in the air condenses and forms frost.

Option B is incorrect because there is typically less water vapor in the air inside your home than in the air outside. This is because the air inside your home is heated and dry, while the air outside is cold and moist.

Option C is incorrect because there is typically more water vapor in the air outside your home than in the air inside your home. This is because the air outside is cold and moist, while the air inside your home is heated and dry.

Option D is incorrect because the inside of the pane is colder than the outside. This is why frost forms on the inside of the windowpane, rather than the outside.