Explain why nanoparticles of a substance can have different properties compared to a bulk sample of the same substance, and suggest one reason why the use of nanoparticles in consumer products may cause concern.

Nanoparticles have a much larger surface area to volume ratio than bulk materials, so a greater proportion of atoms are exposed on the surface. This increased surface area can give rise to new or enhanced physical and chemical properties, such as higher reactivity, different optical behaviour or altered catalytic activity, compared with the bulk substance.

Because nanoparticles are only 1–100 nm in size, they can penetrate biological barriers such as cell membranes or the skin. This means they may enter the body or the environment more readily than larger particles.

The long‑term health or environmental effects of nanoparticles are not yet fully known or tested, so their safety is uncertain, which raises concerns about their widespread use in consumer products.