A clear liquid from a flask is poured into another clear liquid in a beaker. Which of the following results of this procedure would indicate that a chemical
change has occurred?
The level of the substance in the beaker is higher after the other liquid is added.
A yellow solid forms and then settles to the bottom of the beaker.
Small white crystals are left behind in the flask that held the first liquid.
The mass of the combined liquids is greater than either original liquid.

explanation:

metals have excess of electrons whereas non-metals have deficiency of electrons. thus, in order to gain stability metals easily donate their electrons to the non-metals.

for example, electronic configuration of sodium is and electronic configuration of phosphorous is .

when a phosphorous atom and sodium atom combine together then sodium will donate is extra one electron to the phosphorous atom. as a result there will be formation of ionic bond between sodium and phosphorous.

the reaction will be as follows.

there, are three sodium sodium atoms and each of them will donate its one extra electron to phosphorous atom. thus, the sub-shell of phosphorous gets completely filled.  

thus, we can conclude that electrons are transferred from atoms of sodium to atoms of phosphorous. this transfer makes the sodium atoms donate one electron and the phosphorous atoms to gain one electron. as a result, the sodium and phosphorus atoms strongly attract each other.

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