Answer: C. Convection currents in the asthenosphere.
Explanation: Most geologists think that the movement of Earth's plates is caused by convection currents in the asthenosphere.
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Answer:In chemistry, a valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
Explanation: hope this helped
Answer:- A. 
is not the correct formula.
Explanations:- Charge for Ba is +2 and charge for O is -2, Here the charges are in equal and opposite so their ratio is 1:1 and hence the formula must be BaO and not .
Rest of the formulas are correct as charge for Ca is +2 and charge for N is -3 . On criss cross we get the formula 
.
Charge for K is +1 and charge for Cl is -1 and so KCl is correct.
Charge for Li is +1 and that for S is -2. On criss cross we get the formula 
.
They added tubes thats the answer
