Explanation:

When air is cold, it becomes denser and tends to sink. This creates a downward flow of air, known as a cold downdraft. The paper snake, being lightweight, is easily affected by this downdraft and moves in the opposite direction, which is upwards.

Reasoning:

When the air is cold, it contracts and becomes denser. This denser air sinks down towards the ground. As a result, there is a downward flow of air. The paper snake, being light, is more affected by this downward flow of air.

Effect on the Paper Snake:

The downward flow of air exerts a force on the paper snake, causing it to move in the opposite direction, which is upwards. This happens because the force of the air pushing downwards is greater than the force of gravity pulling the snake downwards. As a result, the snake moves upwards.

Direction of Movement:

The paper snake moves in the direction opposite to the flow of air, which is upwards. This is because the force of the downdraft is greater than the force of gravity acting on the snake. Therefore, the correct answer is option 'B', which is anti-clockwise.

Conclusion:

In summary, when the air is cold, it becomes denser and sinks towards the ground, creating a downward flow of air. The paper snake, being lightweight, is affected by this downdraft and moves in the opposite direction, which is upwards. Therefore, the correct answer is option 'B', anti-clockwise.