It is very difficult to say without knowing more about those particular set of keywords.

What position in google are you ranking for for those 2 keywords? And when you say you are not ranking for the other 8, do you mean they are not in the top 1000 in google at all?

One possible and common reason (off the top of my head), is that the 2 keywords you are ranking for a much easier to rank for than the other 8, but that is a guess without knowing more :-)

Hi thanks for your reply..
Acctually i am looking to get rankings under 100 in google but one of my 2 keyword get ranks under 100 and i havnt search for more ranks in google. But getting ranks in google will bring traffic to my website. ?

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A lot of reasons can be mentioned in here, for example how competitive those terms are and the number of domains which are competing in your web niche. Even the age of your domain could be an important issue to mention in here and how your site has been developed and its structure. For example, when it comes to targeting ten keywords, similar to the practice you are currently doing, it is better to use internal pages of your site as well as front section to have ranks.

It is not a great idea to use only homepages of websites to enter the SEO world because normally each page could be optimized professionally for a few terms, but using inner sections of websites, it is possible to expand the keywords lists to dozens and even hundreds of various terms. You may consider to add some new pages to your website, optimized for extra list of keywords and then build links for them, this will take time to generate results but can work most of the time.