A 31.5 g wafer of pure gold initially at 69.4 ∘C is submerged into 63.4 g of water at 27.4 ∘C in an insulated container.

What is the final temperature of both substances at thermal equilibrium?

The final temperature of both substances at thermal equilibrium is 301.0 K

Explanation:

As we know that,  

        .................(1)

where,

q = heat absorbed or released

= mass of gold = 31.5 g

= mass of water = 63.4 g

= final temperature = ?

= temperature of gold =

= temperature of water =

= specific heat of gold =

= specific heat of water=

Now put all the given values in equation (1), we get

The final temperature of both substances at thermal equilibrium is 301.0 K

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.

i'm pretty sure its b i might be wrong though!