How many moles are in 68 grams of potassium sulfide (K2S)?

No of moles of potassium sulfide (K2S)=0.61671moles

Explanation:

No of moles is given as   Mass/ molar mass

Here Mass of potassium sulfide (K2S) =68 grams

Molar mass of potassium sulfide (K2S)  = 39.0983 x 2 + 32.065 =110.2616 g/mol

No of moles =68 grams /110.2616 g/mol

=0.61671moles

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.

it would be b. 6co2 + 6h2o --> c6h12o6 + 6o2