<span>It can be used by scientists everywhere its important to have the International System of Units.</span>
Your answer is B and the element is Carbon
So what your looking for is matching isotopes. Isotopes are elements that are the same in amount of protons but different in mass meaning different number in neutrons. Because when you add the total protons and neutrons together you get your atomic mass. So this can be written as X=said element, top number above=different atomic mass, bottom number below=atomic number. Hope this help!!
Be careful because answer A has same masses but different atomic numbers so different atoms(elements)!!!
The balanced half-reaction: Cr²⁺⁺(aq) → Cr⁴⁺(aq) + 2e⁻.
Chromium(II) cations two electrons and became chromium(IV) cations.
<span>Oxidation
reaction is increasing of oxidation number of element, because element or
ion lost electrons in chemical reaction.
</span><span>Reduction is lowering
oxidation number because element or ions gain electrons.</span>
Explanation:
When an element is displaced by another element in a compound then it is known as a single displacement reaction.
For example, 
is a single displacement reaction.
Similarly when a hockey player has the puck in the corner of the rink. An opposing player muscles him aside and emerge with the puck displays that a single player is displacing a person.
Thus, we can conclude that this situation is most analogous to single displacement reaction.
