Metalloids are elements that exhibit properties of both metals and non-metals. They are located on the periodic table between the metals and non-metals and have characteristics of both categories.
Option 1, alloys of alkali metals with other metals, is not correct. Metalloids are not specifically alloys of alkali metals with other metals, but rather a separate category of elements.
Option 2, colloids of metals, is also incorrect. Colloids are a type of mixture, where particles are dispersed in a medium. Metalloids are not colloids, but individual elements with specific characteristics.
Option 4, metals heavier than lead, is not accurate. Metalloids can be found throughout the periodic table and are not limited to being heavier than lead.
Therefore, the correct answer is option 3, elements having some properties of both metals and non-metals, as this best describes and defines metalloids.