I have just started a blog on my site using K2 blog category. But I have found that google is not indexing the pages. Google has indexed only the site.com/blog But has not indexed the post pages or article pages individually. What the problem may be?

Are you using a sitemap plugin?

Make sure it offer support for K2 and it has a setting for indexing K2 items apart from menu items as well.

I'm not using any sitemap plugin.
However I've already uploaded a sitemap to my site and told google about it. This uploaded sitemap only contains my basic pages and don't include k2 blog pages.
I tried to create a new sitemap using online services. But all sites create sitemap only for my basic pages and blog pages are not included in sitemap. They can not fetch blog pages.
I've two menus. One for my basic pages including home page. Other is for k2 blog. Both menus appear only on their own pages. No link to k2 blog from home page or other basic pages. Does it is effecting any way?

Yes it does.

If your sitemap does not include your K2 items and Google cannot find any links for it then it won't get indexed.

There is a sitemap extension which offers a K2 plugin called xmap. Maybe you should try it.

Thanks admin,
Can I also create sitemap manually?

It will take too much time. I suggest you use a Joomla! extension instead.