Answer:
Dmitry Mendeleev
Explanation:
Around 1869 a Russian scientist, Dmitry Mendeleev formed what is now known as the periodic table or chart. The Mendeleevian periodic table was based on the atomic weights of elements using the periodic law. The periodic law states that "chemical properties of elements are a periodic function of their atomic weights".
The modern periodic table was re-stated by Henry Moseley in the 1900s. He changed the basis of the periodic law to atomic masses.
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.
The substance that conducts electricity is 
dissolved in water.
So, option A is correct one.
When the sodium chloride dissolve in water , the sodium atoms and chlorine atoms separates under the presence of water molecules and exist as sodium cation and chloride anion . Now , they are free to move around in the water as positively and negatively charged ions . This separation of charge allows the solution to conduct electricity.
The solid and solid sugar does not conduct electricity because it is not dissolve in water . Similarly, sugar dissolved in water does not conduct electricity .
to learn more about conduct electricity.
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