What can be measured using a dioptre meter?

Under what condition in an arrangement of two plane mirrors,will the incident ray and the final reflected ray always be parallel to each other,regardless of the angle of incidence? Show the same with the help of a diagram.

Where should an object be placed in front of a convex lens to obtain an image on the same side as the object?

$(i)$ Under what condition does a concave mirror produce a virtual and magnified image? Draw a labelled ray diagram to show the formation of the image in the above case. Also,state the position of the object to produce a magnified and real image.
$(ii)$ $A$ ray of light moving along the principal axis is falling on a concave mirror. Draw the path of the reflected ray. Also,state the values of the angle of incidence and reflection in this case.

Where should an object be placed in front of a concave mirror to obtain its image at the same position?

What is the speed of light waves in a vacuum in units of $km/s$?