Answer:
A metallic bond is formed by the attraction between positively charge metal ions and the electrons around the ions.
Explanation:
Hope this helps.
There are many ways which can <span>lead us to believe a chemical reaction has occurred. I am discussing few of them.
Change in Color:
Few reactions proceed with the change in colour. When Bromine Water (yellow-Brown) is treated with unsaturated compounds, the color disappear as the reaction is completed.
Gas Production:
Some reactions proceed with the elimination of gas i.e. CO</span>₂ , H₂, N₂, H₂O e.t.c.
Temperature Change:
Some reactions evolve or absorb heat when proceed. This change is the evidence of progress of reaction.
Thin Layer Chromatography:
Very important technique in detecting the progress of reaction by determining the number of spots for UV active compounds on TLC plate. Even non UV active compounds can be detected by using other locating agents.
Instrumental Techniques:
Modern techniques like IR, MS, NMR, UV spectroscopy can be used to detect the progress of reaction.
Answer:
The answer to your question is below
Explanation:

I believe the answer is observation of the elements
The answer should be B, it reacts in air to form a green layer.
Chemical properties means that how the substance that reacts with other substance to produce new substances. Usually it cannot be measured or observed just with the substance itself.
From all the options above, only B is a reaction. The green layer formed is a new substance produced by copper and air. It involves a chemical change.
Other options like boiling points or state of matter, these are physical properties. They do not require it to react to other substances and the can be measured and observed easily.