Which statement describes a physical change?

• A. Hydrogen gas reacting with oxygen to form H_2O.
• B. Ice melting into liquid water.
• C. Sodium reacting with chlorine to produce NaCl.
• D. Iron rusting to form Fe_2O_3.

Answer: (B)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: A physical change affects the form or state of a substance without changing its chemical identity, while a chemical change results in the formation of new substances with different chemical properties.
2. Analyze each option to determine if it involves a change in chemical composition or just a change in physical state.
3. For the option 'Hydrogen gas reacting with oxygen to form H_2O,' recognize that this is a chemical change because new chemical bonds form, producing water, a different substance.
4. For the option 'Ice melting into liquid water,' identify this as a physical change because the substance (H_2O) remains the same, only its state changes from solid to liquid.
5. For the options involving sodium reacting with chlorine and iron rusting, note that both are chemical changes since new compounds (NaCl and Fe_2O_3) are formed through chemical reactions.