None is or are

Here's a simple rule of thumbs:

When you use 'none' with a plural noun, it takes a plural form. A plural noun suggests several discrete, countable units (e.g., cars, people, students.) 

• None of the cars in the car park are red.
• None of us are perfect.
• The teacher turned to the students and said "none of you (i.e., the students) have done the homework right."

When you use none with a singular noun, it takes a singular form. 
A singular noun is either not countable (e.g., water, art) or suggests a whole unit rather than many discrete units (e.g., money, food.) 

• None of the water is polluted.
• None of my art was selected for the exhibition.
• None of their money was spent on junk food.