  A stellar population synthesis model, suitable for comparison with Giant
Extragalactic HII Regions (GEHRs), is constructed incorporating the recent
developments in modelling stellar evolution by Maeder and co-workers and
stellar atmospheres by Kurucz. A number of quantities suitable for comparison
with broad band data of GEHRs in visible and near infrared parts of the
spectrum are synthesized in addition to the hydrogen and helium ionizing photon
production rates at solar metallicities, for three scenarios of star formation
--- (i) Instantaneous burst (IB) (ii) Continuous star formation (CSF) and (iii)
Two bursts of star formation, with the older burst rich in red supergiants. For
IB case, evolution of colors shows three distinct phases --- an initial steady
blue phase, followed by a red bump (5--15~Myr) and another steady phase with
colors intermediate to the earlier two phases. CSF colors asymptotically reach
peak values at $\sim 10$~Myr, never reaching the reddest IB colors. Ionizing
photon production rate falls off by an order of magnitude in 6~Myr for IB,
where as it almost remains constant for CSF model. Two-burst models with burst
separations $\sim 10$~Myr have properties of both IB and CSF, simultaneously
producing the red IB colors and high ionizing photon rate, making such regions
easily distinguishable using optical observations. Flat IMFs result in bluest
colors when the massive stars are on the main sequence and reddest colors
during the red supergiant phase of the evolving massive stars. Errors on the
computed quantities due to the statistical uncertainties inherent in the
process of star formation become negligible for cluster masses in excess of
$10^5$\,\msun.
