Please help it is due today

What is avogadro’s number, and why is it useful

Astudent completes a titration by adding 12.0 milliliters of naoh(aq) of unknown concentration to 16.0 milliliters of 0.15 m hcl(aq). what is the molar concentration of the naoh(aq)? 1)5.0 m 2)0.20 m 3)0.11 m 4)1.1 m

How many lone pairs of electrons are on the central atom of no3- and what is the molecular shape? one, trigonal planar zero, trigonal pyramidal zero, trigonal planar one, tetrahedral one, trigonal pyramidal