**The Definition of Orifice**

An orifice is a small opening or hole through which fluid (such as gas or liquid) can flow. It is typically found in pipes, tanks, or vessels and is used to control the flow rate or pressure of the fluid.

**Factors Determining the Size of an Orifice**

The size of an orifice refers to the diameter or cross-sectional area of the opening. The larger the diameter or area, the larger the orifice. The size of an orifice is determined by the design specifications and requirements of the system in which it is being used.

**The Relationship Between Orifice Size and Flow Velocity**

The size of an orifice is directly related to the flow velocity of the fluid. When the size of the orifice is large, the flow velocity tends to be small. On the other hand, when the size of the orifice is small, the flow velocity tends to be large.

**Explanation of the Statements**

1. The statement "The size of orifice is large" is correct because a large orifice will have a larger diameter or cross-sectional area, allowing for a larger flow rate of fluid. This is due to the fact that a larger orifice provides less resistance to the flow of fluid.

2. The statement "The velocity of flow is large" is incorrect because a large orifice actually results in a smaller flow velocity. This is because the larger opening allows for a greater volume of fluid to pass through, spreading it out and reducing the speed at which it flows.

3. The statement "The velocity of flow is small" is correct. As mentioned earlier, a large orifice allows for a greater volume of fluid to pass through, resulting in a lower flow velocity.

4. The statement "The size of orifice is small" is incorrect because a small orifice will have a smaller diameter or cross-sectional area, which restricts the flow of fluid and increases the velocity. A smaller orifice creates more resistance to the flow of fluid, causing it to flow at a higher speed.

**Conclusion**

In conclusion, an orifice is said to be large when the size of the orifice is large, resulting in a smaller flow velocity. Conversely, an orifice is considered small when the size of the orifice is small, leading to a higher flow velocity.