First problem is of GATE 2014 . This problem is based on TE modes of rectangular waveguide.
Second problem is of GATE 2015. Longitudinal component of magnetic field inside the waveguide is given and one has to find mode of propagation.
Third problem is of GATE 2016 . Rectangular waveguide is given, one has to determine cutoff frequencies of various TE modes and how they are arranged in increasing order of frequencies.