Answer:
OPTION (A) : Testing a rock sample for gold content
Explanation:
For testing a rock sample of gold content you will need a Chemist. To test the material, the sample is rubbed on black stone which will leave a mark on the stone. This mark is tested by applying aqua fortis i.e nitric acid on the mark. If the mark gets dissolve then the material is not gold. If the mark sustain the it is further tested by applying aqua regia i.e nitric acid and hydrochloric acid which will prove the sample is of gold if it gets dissolve on using hydrochloric acid. The purity of the sample can be checked by differing the concentration of the aqua regia and comparing it with the gold material of the known purity.
I believe it will be A. Density, temperature, and viscosity, can be found in water through tests. Hope this helps! Mark as brainly please!
<span>The normal dividing line for soluble/not soluble is 0.1 M.
If a substance, as a saturated solution at room temp and pressure, cannot form a solution concentration of 0.1 M, then it is considered insoluble.
The 0.1 M figure was selected because _most_ substances are either well above that value or well below. Some substances (calcium hydroxide is one? not sure) come close to the 0.1 M dividing line but there are only a very few.</span><span>
but most likely it wont mix</span>
Answer:
0.171 grams of oxygen combined with the metal.
Explanation:

Mass of magnesium oxide produced = 0.421 g
Mass of magnesium metal used = 0.250 g
Suppose reaction completely converts the magnesium into magnesium oxide.
Mass of oxygen combined with magnesium = m
0.421 g = 0.250 g + m
m = 0.421 g - 0.250 g = 0.171 g
0.171 grams of oxygen combined with the metal.