YouTube is very clear about the types of videos you can’t monetize on their platform. Monetization means Google ads can show while someone is watching your video. If he or she clicks on the advert, you are paid. Here are some types of videos you can’t monetize;

Nudity 

Nudity of any degree in part or all of your video will make the video not eligible to make money. Sexually provocative scenes also fall into this class. 

Copyright

Posting other peoples original video content in whole or part on your channel makes the video not monetizable.. The best way to avoid copyright issues is to make sure you own all the rights in the video you create. However in some cases, YouTube still allows you to monetize other peoples content in your video provided you create your own original commentary. 

Violence

Video showing violent or gory scenes, killing of human beings or animals, firearms, etc. is not eligible for monetization.

Hate speech

Videos promoting hate speech,religious intolerance, racism are not eligible for monetization on YouTube.

Nonsensical content

Videos showing content with no educational value or that makes no sense can’t be monetized.

PowerPoint videos

Powerpoint videos refers to videos containing only a series of pictures with little or no voice narrative. These types of videos are difficult to monetize.

Robotic voice

You can monetize a video containing robotic or computerised voice provided you created the write up  for the robotic voice to use. However, using a robotic voice to read from pages of newspapers or text books which you didn’t create  can’t be monetized.

Animals

Videos showing killing,torturing, mating, cutting open of animals can’t be monetized.

Children

Videos showing children subjected to inhuman treatment, or abuse won’t be monetized.

For more on what videos can’t be monetized you can read YouTube Monetization policies