Keep working on providing good content and driving traffic to your site. Google updates their page rankings every few months. You will need to have a good authority site if you want to reach PR 4, especially within the next year.

Alexa is a feminine form of Alexander, which comes from the Greek, Alexandros. It can be broken down into alexo meaning "to defend" and aner, meaning "man"' making both Alexa and Alexander mean defender of man

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Still i hav doubt what is difference between Alexa Rank and Page Rank ?

Alexa rank has nothing to do with Pagerank. Alexa is a service that attempts to estimate traffic levels to internet web sites. Pagerank is a measure Google uses to calculate a site's authority.

Alexa rank improves with the number of visitors that have the Alexa toolbar installed. Pagerank improves with incoming links.

Note that the publicly visible Pagerank that Google shows you is NOT the actual Pagerank they use in their ranking algorithm. The publicly visible PR is outdated by as much as several months.

You should try getting organic traffic as
much as possible rather then getting inorganic
or paid traffic, that will help in better
conversions and increase your page rank.

You need to get a lOT of traffic for alexa ranking
PR can be achieved within 6 months if you get backlinks for high PR page