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.
Heterogenous mixtures can separates due to differences in size of components
An atom's mass is determined by its protons and neutrons.
An atom's charge is determined by its number of protons minus it number of electrons.
Atoms become cations, or positively charged when they lose an electron, and since electrons have a negative charge, they become anions, or negatively charged.
Water is a universal solvent.
Carbohydrates (carbs) are used by the body for energy.
Steroids and triglycerides are lipids.
Proteins that catalyze chemical reactions are called enzymes.
D) + ΔH and +ΔE
Given this is one of the answer choices