Does nitrogen alone protect the planet from solar wind and radiation?

No, it's ozone and the magnetic field which does it.

Nope, Nitrogen does nothing, maybe filter some UV,,it is the magnetosphere doing the work.

No

charged particles are slowed down by the magnetic field (Lorentz-force)

the primary defense is our Magnetic Field.

Nitrogen does a good job of filtering out the Ultra Violet in the Solar Radiation

All gases vary by amount with Nitrogen being the most by percentage

 We and other Animals require Oxygen in order to live and CO2 for plants

Without either Earth could have no life, or even a regulated Temperature and Pressure

Did you know, the Ozone Hole has sealed itself again !!

Lack of CFC's

No.

All nitrogen does is filter the ultraviolet radiation from the star. That is?why people who sunburn. like me. Sunburn faster at higher elevations than they do at sea level. I have direct personal life?experience with that. I grew up in BOTH greater New Orleans an f the Oklahoma panhandle at aroundc3600 feet and I've lived in central Oklahoma at 3100 get for over 2/3 of my life. My last bad sunburn happened in the Rocky Mountains during geology field camp in Colorado at over a mile high. I forgot to put sunscreen on the back of my neck and wore T shirt and baseball hit. That's a major reason I don't Sun bathe or spend much time in the Sun. The other reason is I can still get glare headaches. 

.Earth's magnetic field and atmosphere does NOT stop the solar wind and solar flares  from stripping H2 molecules and He atoms from off the top of the atmosphere or magnetic storms and solar flares causing electrical surges and EMP outages bringing entire electric grids down when there is high demand. Nitrogen is why there are red aurorae.