Question

1. which is a chemical property of sodium? (a) soft metal, easily cut with a knife. (b) melts at a temperature of 90°c (c) forms compounds with chlorine (d) silver - colored metal. 3. which statement describes a chemical property of hydrogen gas? (a) hydrogen gas burns in air. (c) hydrogen gas has a density of 0.00009g/cm³. (b) hydrogen gas is colorless. (d) hydrogen gas has a boiling point of - 250°c. 2. which choice is one chemical and one physical change? (a) freezing and melting (b) freezing and evaporation (c) burning and rusting (d) dissolving and cooking

Explanation:

Step1: Recall chemical and physical properties

Chemical properties involve changes in the chemical composition of a substance, while physical properties can be observed without changing the substance's chemical identity.

Step2: Analyze question 1

For sodium, being soft and easily cut with a knife is a physical property. Melting at a certain temperature is also a physical property. Forming compounds with chlorine is a chemical property as it involves a chemical reaction. Silver - colored is a physical property. So the chemical property of sodium is forming compounds with chlorine, answer is (c).

Step3: Analyze question 2

Freezing and melting are physical changes as they only change the state of matter without altering the chemical composition. Burning and rusting are chemical changes as new substances are formed. Dissolving and cooking can be chemical changes (cooking often involves chemical reactions). Evaporation is a physical change. So a chemical change is burning and rusting (c), and a physical change is freezing and melting (a).

Step4: Analyze question 3

Burning in air is a chemical property of hydrogen gas as it involves a chemical reaction with oxygen in air. Having a certain density, being colorless, and having a boiling point are physical properties. So the chemical property of hydrogen gas is hydrogen gas burns in air, answer is (a).

Answer:

1. (c) forms compounds with chlorine
2. Chemical change: (c) burning and rusting; Physical change: (a) freezing and melting
3. (a) Hydrogen gas burns in air