How can you determine if a chemical change has occured

There are several ways to know if a chemical change has occurred. The following is an indication that a chemical change has occurred

1. Change of composition - wood turning to ash when burned.

2. Change of color - For example, during titration, we know that the reaction has occurred by a change in colour from orange to pink when we used methyl orange as indicator., rusting of iron.

3. Change in temperature or energy, such as the production (exothermic or loss endothermic) of heat.

4. The decomposition of organic matter for example, the decay of dead plant or animal

5. Light and/or heat given off: For example, potassium react explosively with water releasing a large amount of heat

6. When the change is difficult to reverse. For example, after burning wood to produce ash, we can not get back the wood again.

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3

i think that the answer is c