Explanation:
A concave lens is a type of lens that is thinner at the center and thicker at the edges. It is also known as a diverging lens because it causes the light rays to diverge or spread out. The focal length of a lens is the distance between the lens and the point where the light rays converge or appear to converge.

Negative Focal Length:
The focal length of a concave lens is always negative. This is because the concave lens causes the light rays to diverge or spread out. As a result, the point where the light rays appear to converge is behind the lens. This point is called the virtual focus, and it is located on the same side of the lens as the object. The distance between the lens and the virtual focus is the focal length, which is always negative for a concave lens.

Real or Virtual Image:
A concave lens can form both real and virtual images depending on the position of the object. If the object is located beyond the virtual focus, the image formed is real, inverted, and smaller in size than the object. If the object is located between the lens and the virtual focus, the image formed is virtual, erect, and larger in size than the object.

Positive Focal Length:
In contrast, a convex lens is thicker at the center and thinner at the edges. It is also known as a converging lens because it causes the light rays to converge or come together. The focal length of a convex lens can be positive or negative depending on the position of the object. If the object is located beyond the focal point, the image formed is real, inverted, and smaller in size than the object. In this case, the focal length is positive. If the object is located between the lens and the focal point, the image formed is virtual, erect, and larger in size than the object. In this case, the focal length is negative.

Yes d is correct becoz f is distance btw p and focus so as the obj is always placed infront of mirror to LHS so by sign convention it's always -ve