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Q15. A black object may look black, but, technically, it may still be reflecting some light. For example, a black pigment results from a combination of several pigments that collectively absorb most colors. If appropriate proportions of three primary pigments are mixed (red ,yellow and blue), the result reflects so little light as to be called "black." In reality, what appears to be black may be reflecting some light.
Q16. Rods are more in number around periphery of retina while cones are more concentrated near central part of retina, i.e. in macula. Both cells are packed with photoreceptive opsin proteins, rhodopsin in rod and iodopsin in cone . Both the cells get stimulated by light and develop electrical signal in response to light.