Matter is the substance that we can see and observe.

true
false

I'd say true. 
Matter is a physical substance that occupies space.
Lets say you put random stuff in a box. That stuff is matter, filling the box.
Its common to say that matter is everything around you. You can see everything around you (almost).

Hbr dissociates to form h+ and br-ca(oh)2 dissociates to form ca2+ and 2oh-the h+ and oh- react to form waterassuming the reactants are dissolved in water, the net reaction is h+ + oh- —> h2oif you’re asked to show all components of the reaction, the complete reaction is 2hbr + ca(oh)2 —> cabr2 + 2h2o