Which answer matches this clue: the Turin-born scientist whose law relates gas volume to the number of its molecules?

• A Stanislao Cannizzaro
• B Luigi Galvani
• C Evangelista Torricelli
• D Amedeo Avogadro ✓

Amedeo Avogadro proposed in 1811 that equal volumes of gases contain equal numbers of molecules; Avogadro's constant is named in his honour.