To obtain a real and enlarged image of an object, it should be placed between the principal focus and twice the focal length in front of a convex lens.

Option 1: Placing the object at twice the focal length will result in a real and inverted image, but the size of the image will be the same as the object. Therefore, it does not meet the requirement for an enlarged image.

Option 2: Placing the object at infinity will result in a real and inverted image, but it will be highly diminished in size. Again, this does not fulfill the condition for an enlarged image.

Option 4: Placing the object beyond twice the focal length will result in a real and inverted image, but it will be further reduced in size. Hence, it does not satisfy the requirement for an enlarged image.

Therefore, the correct option is 3, which is placing the object between the principal focus and twice the focal length. This positioning will create a real and enlarged image of the object in front of the convex lens.