The correct answer is False.
When two unsaturated air masses mix horizontally, the resulting mixture can be saturated if the relative humidity of the air masses is greater than 100%. This is because the relative humidity is a measure of the amount of water vapor in the air relative to the maximum amount of water vapor that the air can hold at a given temperature. When two air masses mix, the water vapor from both air masses is mixed together, and the relative humidity of the resulting mixture can be greater than 100% if the air masses have different temperatures.
For example, if one air mass has a temperature of 20 degrees Celsius and a relative humidity of 80%, and the other air mass has a temperature of 10 degrees Celsius and a relative humidity of 60%, then the relative humidity of the resulting mixture will be greater than 100%. This is because the air mass with the higher temperature can hold more water vapor than the air mass with the lower temperature. When the two air masses mix, the water vapor from the air mass with the higher temperature will be added to the air mass with the lower temperature, and the relative humidity of the resulting mixture will be greater than 100%.
In addition, the relative humidity of the resulting mixture can also be greater than 100% if the air masses have different amounts of water vapor. For example, if one air mass has a water vapor content of 10 grams per kilogram of air, and the other air mass has a water vapor content of 15 grams per kilogram of air, then the relative humidity of the resulting mixture will be greater than 100%. This is because the air mass with the higher water vapor content will have a higher relative humidity than the air mass with the lower water vapor content. When the two air masses mix, the water vapor from the air mass with the higher water vapor content will be added to the air mass with the lower water vapor content, and the relative humidity of the resulting mixture will be greater than 100%.