I'm on a test someone ! what is a normal force?

it acts against an object slowing it down.

it acts parallel to an object.

it acts with an object adding to its speed.

it acts perpendicular to an object.

answer: it acts perpendicular to an abject.

answer:

its "d"   -   "it acts perpendicular to an object."

in mechanics, the normal force is the component of a contact force that is perpendicular to the surface that an object contacts. for example, the surface of a floor or table that prevents an object from falling.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.