First of all, for all newcomers in the field of SEO- Blogging as well as Digital Marketing -I just want to confirm that there is No Right Answer to this question. You cannot really determine exact number of keywords suitable for a page. What you could do is to guess how many keywords you could rank for this page.

These are some of the factors that may help you get the best estimates for every page you are looking to rank on Google:

1. Page Type: First, you should know if we are dealing with a page from a blog, an e-commerce site or just a regular website. Each one of them has different approach to find how many keywords you could rank for that particular page.

Blog: If the page you are looking to get ranked is a blog post, you must target only one focus keyword. You could increase the focus keyword density by trying to rank it on long tail words as well but your real focus should stay on your Focus Keyword.

E-commerce: A little tricky but a very popular phenomenon is to rank various products on e-commerce website. For this type of pages, you could use as much keywords as you want until you have at least 100 words to go alongside each focus keywords.

Static sites: For basic static sites, and home/landing pages, you could use more than one keywords but all focus keywords should be inter-related. These keywords should be connected but should also be backed by other long tail words too.

2. Page-Size: When it comes to finding keywords on the basis of the length of the page, one should always commit to the 1000:1 rule. If we are writing a blog post, we should try to rank one focus keyword for every 1000 words of the article.

3. Website Structure: Ranking more than one keyword for a single page depends on how your site has been structured. In a well-structured and categorized site, you could try to rank multiple keywords.

But, please never use excessive number of keywords for any page as it may lead into the confusion from both users’ as well as search engine's end.