Aship is a stationary for some time in an ocean. the ocean is 10,500 m deep. an engineer from the ship sends a signal straight down into water. how long will it take for the echo to reach him? ( velocity of sound in water : 1.5 km/s)

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.

explanation:

the answer is c.the valence of the atoms combine .