Question

What does ++ mean in science & give 1 example.

Answer 1

it means that the atom or the group of atoms became positive ion by losing two electrons Ex.
${be}^{ + 2} \: or \: {mg}^{ + 2}$

Answer 2

++ can have different meanings in Math, Accounting and other subjects. As the question is about chemistry, ++ means a neutral atom or molecules has lost 2 electrons.  It now has a double positive charge. An example is Calcium ion, Ca++.