Is the object a pulsar We have a star having 1.8 solar mass. Justify any four means (measurable/ observed properties) by which you can identify that the object is a Pulsar and not a white dwarf or a Black Hole.


So one obvious property would be the mass. Since mass > 1.4 solar mass, we can say it is not a white dwarf. 

Also the mass is less than 3 solar mass, hence its not a black hole (I'm speaking loosely over here). 

Also from periodic radiation patterns, we can say that the object might be a pulsar. 

I need help with 2 other means to categorize this object.
As you said, the mass range of the object indicates that it could be a neutron star, rather than a black hole.
But also the density of the object is a clue. The density of a neutron star is much higher than that of a stable white dwarf.
Extremely regular electromagnetic pulses have to be observed. Known pulsars have a pulse period between 1.4 ms and 8.5 seconds. 
The wavelength of the pulses is in the radio range.
Pulsars slow down gradually, at a known rate, so you can measure how the pulse period evolves over time, and check that is compatible with the slow-down rate of a pulsar.


Adapted from this page