An electron in a sodium atom gains enough energy to move from the second shell to the third the sodium atom becomes

When an electron in a sodium  atom gains  enough  energy  to move from  the second shell  to  the third  the sodium atom  becomes  

 an  atom in excited state

Explanation

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.