Question

what do these two changes have in common?
filtering air to remove dust and pollen
a crayon melting in the sun
select all that apply.
both are only physical changes. both are chemical changes.
both are caused by heating. both are caused by cooling.

Explanation:

• Filtering air to remove dust and pollen: This is a physical change as it involves a separation process (using a filter) without altering the chemical composition of the substances (air, dust, pollen).
• A crayon melting in the sun: Melting is a physical change. When a crayon melts, its state changes from solid to liquid, but the chemical composition of the wax (main component of a crayon) remains the same. There is no new substance formed, which is a key characteristic of a physical change.
• Why other options are incorrect:
• Both are chemical changes: In chemical changes, new substances are formed. Since no new substances are formed in either filtering air or crayon - melting, this option is wrong.
• Both are caused by heating: Filtering air to remove dust and pollen is not caused by heating. It is a mechanical (physical) separation process.
• Both are caused by cooling: A crayon melts in the sun (due to heat from the sun), not because of cooling. And filtering air is not related to cooling.

Answer:

A. Both are only physical changes.