  The first photometric, spectroscopic, and period variation studies of
neglected short-period eclipsing binary V2840 Cygni are presented. High Mass
Ratio Contact Binaries, especially those in the weak-contact configuration are
vital while probing into the evolutionary models of CBs using stellar
parameters. The photometric solutions reveal the weak-contact nature of V2840
Cygni with a high mass ratio ($\sim1.36$), motivating us to investigate the
nature of such binaries. The period variation study of V2840 Cygni spanning for
15 years shows a secular period decrease at a rate of
$\sim5.5\times10^{-7}$d/yr indicating mass transfer between the components. The
superimposed cyclic variation provides a basic understanding of the possible
third body (P$_3$ $\sim8$ yr, m$_3$ $\sim0.51$M$_\odot$). Following the derived
parameters, the evolution of the system is discussed based on Thermal
Relaxation Oscillation (TRO) model. It is found that V2840 Cygni falls in a
special category of HMRCBs, that validates TRO. To characterise the nature of
HMRCBs, a catalog of 59 CBs with high mass ratios has been compiled along with
their derived parameters from the literature. For all the HMRCBs in the study,
a possible correlation between their contact configuration and observed period
variations for relative log\emph{J$_{rel}$} is discussed. The spectroscopic
study of V2840 Cygni provides evidence of the presence of magnetic activity in
the system and the existence of ongoing mass transfer which is additionally
deduced from the period variation study. The LAMOST spectra of 17 HMRCBs are
collected to interpret the stellar magnetic activity in such systems.
