Density is m/V. Also, 1 liter = 1000 . So, we get 0.890/(5*1000) = g/cm^3. You can convert this to kg/m^3 as well by multiplying it by 10. Depends which one you want.
Moles of Zn present= 2.36/65.4= 0.0361 moles Therefore maximum moles of ZnO= 0.0722 Mass of one mole of ZnO= 81.4 Mass of ZnO produced= 0.0722 x 81.4= 5.87g
