Sodium loses an electron and chlorine gains an electron. Simply put. It's a little more complicated, but that's what i think they're looking for.
The red semicircle shown in the weather chart represents warm front.
Answer:
The temperature will decrease
Explanation:
the particles spread out while releasing heat
Answer:
(A) 
Solubility will increase.
(B) 
Solubility will decrease.
(C) 
Solubility will decrease.
Explanation:
a) According to Le Chatelier's Principle when a change is introduced in a reaction system at equilibrium, the system responds by the reaction shifting in the direction to counter the change introduced.
When the change introduced is addition of acid, some 
are consumed due to it and the system would respond by reaction shifting towards creation of more in the system by increased dissolution. Thus solubility increase.
(b) When are added, the reaction shifts to counter the change introduced of increased by shifting to side that decreases the increased . That happens by reaction shifting towards some 
precipitating back. Hence solubility decreases.
(c) The change introduced is addition of 
which will be countered by reaction shifting to side that decreases increased 
, which happens by some 
precipitating back. Hence solubility decreases.
