Option 1: This states that the lens is concave and has a focal length of 0.5 metre. However, the correct answer states that the lens is convex. Therefore, this option is incorrect.

Option 2: This states that the lens is convex and has a focal length of 2.0 metre. However, the correct answer states that the lens has a focal length of 0.5 metre. Therefore, this option is incorrect.

Option 3: This states that the lens is convex and has a focal length of 0.5 metre. This matches the information provided in the question, which states that the lens has a power of +2.0 Dioptre. A positive power signifies a convex lens, and the focal length of a lens is the reciprocal of its power. Therefore, this option is correct.

Option 4: This states that the lens is concave and has a focal length of 2.0 metre. However, the correct answer states that the lens is convex. Therefore, this option is incorrect.

In conclusion, the correct statement is that the lens is convex and has a focal length of 0.5 metre.