  We report on the variation in the single-pulse emission from PSR J1900+4221
(CRAFTS 19C10) observed at frequency centered at 1.25 GHz using the
Five-hundred-meter Aperture Spherical radio Telescope. The integrated pulse
profile shows two distinct components, referred to here as the leading and
trailing components, with the latter component also containing a third weak
component. The single-pulse sequence reveals different emissions demonstrating
as nulling, regular, and bright pulses, each with a particular abundance and
duration distribution. There also exists pulses that follow a log-normal
distribution suggesting the possibility of another emission, in which the
pulsar is radiating weakly. Changes in the profile shape are seen across
different emissions. We examine the emission variations in the leading and
trailing components collectively and separately, and find moderate correlation
between the two components. The inclination angle is estimated to be about
7{\deg} based on pulse-width, and we discuss that nulling in this pulsar does
not seem to show correlation with age and rotation period.
