In this question, we are asked to identify which substance is NOT a mixture. A mixture is a combination of two or more substances that are physically combined and can be separated by physical means.

Option 1: Ice. Ice is pure water in solid form. It is not a mixture because it is made up of only one substance, which is H2O. Therefore, ice is not a mixture.

Option 2: Ice-cream. Ice-cream is a mixture because it is made up of various ingredients such as milk, sugar, cream, and flavorings. These ingredients are physically combined to form a mixture, which can be separated.

Option 3: Air. Air is a mixture because it is made up of different gases such as nitrogen, oxygen, carbon dioxide, and trace amounts of other gases. These gases are physically combined and can be separated by methods such as fractional distillation.

Option 4: Honey. Honey is a mixture because it is made up of various carbohydrates, water, enzymes, and trace amounts of other substances. These components are physically combined and can be separated by methods such as filtration and centrifugation.

Therefore, the correct answer is option 1: Ice, as it is not a mixture.