As far as I know keyword density is not a ranking factor so that isn't something you need to worry about. Just write naturally. No need to stuff, repeat or overdo it. On the other hand having a relevant, focused title tag is far more important. Therefore the keyword you target needs to be prominently featured in the page's title tag. Also make sure your content is unique, and not published elsewhere. And minimum 300 words of text - the more the better. If you really want to know what density is acceptable check out the top ranking sites for the keyword you're targeting and use a tool like http://www.zippy.co.uk/keyworddensity/ to see what the density for the keyword is on these sites.
2-3 is good according to me. Of course it depends on the niche and the content you write! Just do NOT overdo it
Keyword density is the percentage of the number of times a keyword appears on a page divided by the total number of words in that page. There is no ideal or exact percentage for better ranking. 1-3% of keyword density along with semantic keywords works best for me.
1-3% is the good keyword density. You can measure keyword density through this trick: Total number of keywords/ Total number of words) * 100. According to my opinion you focus on content's quality and don't repeat keyword multiple time, use only where it applicable.
There is no standard density but most commonly 1 to 3% is recommended. Best thing to do would be use keywords in natural way and do not over stuff it.