This is the second paper of a series reporting the results from the PopStar evolutionary synthesis models . Here we present synthetic emission line spectra of H ii regions photoionized by young star clusters , for seven values of cluster masses and for ages between 0.1 and 5.2 Myr . The ionizing Spectral Energy Distributions ( SEDs ) are those obtained by the PopStar code ( Mollá , García-Vargas & Bressan , 2009 ) for six different metallicities , with a very low metallicity set , Z=0.0001 , not included in previous similar works . We assume that the radius of the H ii region is the distance at which the ionized gas is deposited by the action of the mechanical energy of the winds and supernovae from the central ionizing young cluster . In this way the ionization parameter is eliminated as free argument , since now its value is obtained from the cluster physical properties ( mass , age and metallicity ) and from the gaseous medium characteristics ( density and abundances ) . We discuss our results and compare them with those from previous models and also with a large and data set of giant H ii regions for which abundances have been derived in a homogeneous manner . The values of the [ OIII ] lines ( at \lambda \lambda 4363 , 4959 , 5007Å ) in the lowest metallicity nebulae are found to be very weak and similar to those coming from very high metallicity regions ( solar or over-solar ) . Thus , the sole use of the oxygen lines is not enough to distinguish between very low and very high metallicity regions . In these cases we emphasize the need of the additional support of alternative metallicity tracers , like the [ SIII ] lines in the near- IR .