Question

1. a mixture of salt, sand, and water passes through a filter. the residue (the substance stuck in the filter) is a: (note: the formulas are salt = nacl, sand = sio₂, water = h₂o) heterogeneous mixture homogeneous mixture compound element

Explanation:

• A compound is a substance formed when two or more elements chemically bond together. An element is a pure substance that cannot be broken down into simpler substances. Since the residue is sand (\(SiO_2\)), which is a compound made of silicon and oxygen atoms chemically bonded, but wait - no! Wait, the mixture is salt (\(NaCl\)), sand (\(SiO_2\)), and water (\(H_2O\)). When filtered, salt (\(NaCl\)) dissolves in water (\(H_2O\)) and passes through the filter. Sand (\(SiO_2\)) does not dissolve in water and is retained as the residue. Sand (\(SiO_2\)) is a compound (but if we consider the nature of the residue in terms of the mixture concept - no, wait, no. Wait, actually, the question is about the nature of the residue. The residue is sand. But wait, no - wait, no! Wait, hold on. Wait, the original mixture: salt (dissolves in water - so salt + water is a homogeneous mixture), sand does not dissolve. When filtered, the filtrate is salt - water (homogeneous mixture), the residue is sand. But sand (\(SiO_2\)) is a compound. But wait, no - wait the options: heterogeneous mixture (a mixture where components are not uniform), homogeneous mixture (uniform), compound (two or more elements chemically combined), element (single type of atom). But wait, no - hold on, no! Wait, the problem is: when you filter a mixture of salt (NaCl - dissolves in water), sand (\(SiO_2\) - does not dissolve), and water. The residue is sand. But sand (\(SiO_2\)) is a compound. But wait, no - wait the options. Wait, no! Wait, hold on, maybe a mistake. Wait, no - wait, the question is: the residue (substance stuck in filter). If the mixture is salt + sand + water. Salt dissolves in water (so salt - water is a solution - homogeneous). Sand does not. When filtered, sand (residue) is a compound (\(SiO_2\)). But wait, the options: heterogeneous mixture (a mixture). But sand (\(SiO_2\)) is a compound. But wait, unless the problem has a typo. Wait, no - wait, hold on. Wait, another approach: filtration separates insoluble solids from liquids. The residue is the insoluble part. Sand (\(SiO_2\)) is a compound. A compound is a pure substance (but made of two or more elements chemically combined). But let's check definitions:
• Heterogeneous mixture: components are not uniform (e.g., sand + water before filtering - but residue is sand alone).
• Homogeneous mixture: uniform (like salt - water solution).
• Compound: two or more elements chemically bonded (e.g., \(H_2O\), \(CO_2\), \(SiO_2\)).
• Element: single type of atom (e.g., \(O_2\), \(Fe\)).

Since sand is \(SiO_2\) (silicon dioxide - a compound of silicon and oxygen), the residue (sand) is a compound.

Answer:

compound