Which of the following statements is correct?

An object is placed $60 \ cm$ in front of a convex mirror of focal length $30 \ cm$. $A$ plane mirror is now placed facing the object in between the object and the convex mirror such that it covers the lower half of the convex mirror. What should be the distance of the plane mirror from the object so that there will be no parallax between the images formed by the two mirrors (in $cm$)?

$A$ small fish,$0.4\,m$ below the surface of a lake,is viewed through a simple converging lens of focal length $3\,m$. The lens is kept at $0.2\,m$ above the water surface such that the fish lies on the optical axis of the lens. The image of the fish seen by the observer will be at $\left( \mu_{water} = \frac{4}{3} \right)$

An optical bench has a $1.5 m$ long scale having four equal divisions in each $cm$. While measuring the focal length of a convex lens,the lens is kept at the $75 cm$ mark of the scale and the object pin is kept at the $45 cm$ mark. The image of the object pin on the other side of the lens overlaps with the image pin that is kept at the $135 cm$ mark. In this experiment,the percentage error in the measurement of the focal length of the lens is. . . . .

$A$ biconvex lens $(R_1 = R_2 = 30 \ cm)$ has a focal length equal to the focal length of a concave mirror. What is the radius of curvature of the concave mirror (in $cm$)? (Refractive index of the material of the lens $\mu = 1.6$)

$A$ point object is placed at a distance of $60\, cm$ from a convex lens of focal length $30\, cm$. If a plane mirror is placed perpendicular to the principal axis of the lens at a distance of $40\, cm$ from it,the final image is formed at a distance of: