Consider the following statements : 1. Other than those made by humans, nanoparticles do not exist in nature. 2. Nanoparticles of some metallic oxides are used in the manufacture of some cosmetics. 3. Nanoparticles of some commercial products which enter the environment are unsafe for humans. Which of the statements given above is/are correct ?

The correct answer is D, 2 and 3. Metal-oxide nanoparticles are used in cosmetics and some nanoparticles released into the environment can harm people, but nanoparticles are not made only by humans. A nanoparticle is a particle between about 1 and 100 nanometres across; at this size materials show new optical, chemical and biological properties. Nature produces them in large amounts, in volcanic ash, sea spray, forest-fire smoke, desert dust and even in some living organisms, so statement 1 is false. Zinc oxide and titanium dioxide nanoparticles are widely used in sunscreens and other cosmetics because they block ultraviolet rays while looking clear on the skin. Because they are so small, some engineered nanoparticles can be inhaled deep into the lungs, cross cell membranes and build up in the body, so their release from products is a health concern. Option A is wrong because statement 1 is false. Option B is wrong because it leaves out the true statement 2. Option C is wrong because it includes the false statement 1. Exam tip: Nano = 1–100 nm; zinc oxide and titanium dioxide nanoparticles are used in sunscreens.