The number of rectangular faces of a triangular prism is 3.

Explanation:
A triangular prism is a three-dimensional shape that consists of two triangular bases and three rectangular faces. Let's break down the different faces of a triangular prism to understand why the correct answer is 3.

1. Triangular Bases:
A triangular prism has two triangular bases. These bases are parallel to each other and are congruent triangles. The bases provide stability to the prism and are considered as the top and bottom faces of the shape.

2. Rectangular Faces:
In addition to the triangular bases, a triangular prism also has three rectangular faces. These faces connect the corresponding vertices of the two triangular bases. The rectangular faces are perpendicular to the triangular bases and form the sides of the prism.

3. Total Number of Faces:
To find the total number of faces of a triangular prism, we add the number of triangular bases and the number of rectangular faces. In this case, we have 2 triangular bases and 3 rectangular faces. Therefore, the total number of faces is 2 + 3 = 5.

However, the question specifically asks for the number of rectangular faces, not the total number of faces. So, the correct answer is 3, which represents the number of rectangular faces in a triangular prism.

In conclusion, a triangular prism has 3 rectangular faces. These faces, along with the two triangular bases, make up the total number of faces in the prism.