  In order to recognize a habitable exoplanet from future observed spectra, we
present new model reflected spectra and geometric albedo for modern and
prebiotic (3.9 Ga) Earth-like exoplanets orbiting within the habitable zone of
stars of spectral types F, G, K and M. We compute this for various atmospheric
and surface compositions of the planets. Molecules that are potential
biosignatures and act as greenhouse agents are incorporated in our model
atmosphere. Various combinations of solid and liquid materials such as ocean,
coast, land consisting of trees, grass, sand or rocks determine the surface
albedo of the planet. Geometric albedo and model reflected spectra for a set of
nine potential habitable planets, including Proxima Centauri b, TRAPPIST-1d,
Kepler-1649c and Teegarden's Star-b, are also presented. We employ the opacity
data derived by using the open-source package Exo-Transmit and adopt different
atmospheric Temperature-Pressure profiles depending on the properties of the
terrestrial exoplanets. The model reflected spectra are constructed by
numerically solving the multiple scattering radiative transfer equations. We
verified our model reflected spectra for a few specific cases by comparing with
those published by other researchers. We demonstrate that prebiotic Earth-like
exoplanets and present Earth-like exoplanets with increased amount of
greenhouse gases in their atmospheres scatter more starlight in the optical. We
also present the transmission spectra for modern and prebiotic Earth-like
exoplanets with cloudy and cloudless atmospheres.
