What nuclide is used as the standard in the relative scale for atomic masses?

The correct answer is Carbon-12.

Explanation:

The relative isotopic mass is the relative mass of a given isotope, scaled with carbon-12 as exactly 12 u. There are no other nuclides other than carbon-12 that have exactly an integer number of masses on this scale. This is due to two factors:

1- The different mass of neutrons and protons acting to change the total mass in nuclides with proton/neutron ratios other than the 1:1 ratio of carbon-12.

2- An exact number will not be found if there is a different mass gain/loss than the nuclear bond energy relative to the mean nuclear bond energy of carbon-12.

Have a nice day!

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.