Which of the following statements is true?

Options

A. The north pole of a magnet attracts south pole of another magnet.
B. Atmospheric pressure is the mass of air in a column of unit area.
C. Pressure = Force/Area of surface, here force acts parallel to the surface on which pressure is to be computed.
D. The electrostatic force comes into play when bodies are in contact only.

Explanation

To determine which statement is true, let's analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement:** The north pole of a magnet attracts the south pole of another magnet.

- **Explanation:** This statement is true. In magnetism, opposite poles attract. Therefore, the north pole of one magnet will attract the south pole of another magnet.

### Step 2: Analyze the Second Statement
**Statement:** Atmospheric pressure is the mass of air in a column of unit area.

- **Explanation:** This statement is false. Atmospheric pressure is defined as the force exerted by the weight of air above a unit area. It is not simply the mass of air; rather, it is the weight (force) of the air acting on a surface.

### Step 3: Analyze the Third Statement
**Statement:** Pressure is equal to force per unit area of surface. Here force acts parallel to the surface on which pressure is to be computed.

- **Explanation:** This statement is partially correct but misleading. Pressure is indeed defined as force per unit area (P = F/A), but the force must act perpendicular (normal) to the surface for this definition to hold true. If the force acts parallel, it does not create pressure in the same way.

### Step 4: Analyze the Fourth Statement
**Statement:** The electrostatic force comes into play when bodies are in contact with each other.

- **Explanation:** This statement is misleading. The electrostatic force acts between charged bodies, and it can exist even when the bodies are not in direct contact. Contact can lead to charge transfer, but the force itself does not require contact.

### Conclusion
After analyzing all the statements, the only true statement is:

**True Statement:** The north pole of a magnet attracts the south pole of another magnet.