Equal volumes of 1 molar hydrochloric acid (hcl) and 1 molar sodium hydroxide base (naoh) are mixed. after mixing, the solution will be:

HCl is a strong acid therefore complete ionisation takes place 
HCl ---> H⁺ + Cl⁻
1 mol of HCl dissociates to form 1 mol of H⁺
NaOH is a strong base therefore complete ionisation takes place 
NaOH ---> Na⁺ + OH⁻
1 mol of NaOH dissociates to form 1 mol of OH⁻ ions
equal number of moles of HCl and NaOH will dissociate to give out an equal number of moles of H⁺ and OH⁻ ions.
H⁺ + OH⁻ --> H₂O
equal amount of H⁺ and OH⁻ together forms H₂O
since all the H⁺ and OH⁻ have now reacted to form water molecules the solution now becomes neutral as there are no excess H⁺ ions to make the solution acidic and no excess OH⁻ ions to make the solution basic.

Therefore the solution will be neutral.

Temperature and pressure