Question

question 1
which of the following is a physical change?
○ a pencil is sharpened
○ helium is inert (does not react with anything)
○ hydrogen burns in the presence of oxygen and forms water
○ vinegar reacts with baking soda to produce a gas called carbon dioxide

Explanation:

A physical change alters the form or appearance of a substance without changing its chemical composition. Sharpening a pencil only changes its physical shape. Helium's inertness is a chemical property. Hydrogen burning and vinegar - baking soda reaction are chemical changes as new substances are formed.

Answer:

a pencil is sharpened