Option 1: Solid in solid - This refers to a solid dispersion within another solid, like alloys. This is not the correct answer for cork.
Option 2: Liquid in solid - This refers to a liquid dispersed in a solid, like gels or some food products. This is not the correct description for cork.
Option 3: Solid in liquid - This describes a suspension, which is not what cork is made of.
Option 4: Gas in solid - This is the correct answer. Cork is a solid that contains gas trapped within its cellular structure, making it a colloidal system with gas dispersed in a solid form. This is why cork is light and buoyant.
Explanation:
Cork is a colloidal solution in which gas is trapped in a solid matrix. This makes it a gas in solid colloid. The gas trapped in the cork's cellular structure gives it its lightweight and buoyant properties.