Question: How can I export a specific page in Wordpress?

I want to use a page from one wordpress instance in another wordpress instance, both having same theme.

How can I do this?

Answer: 
Similar to *Ali Raza*'s answer, if you don't want to create an author to export just one page you can

* modify the publish date of the page to a date before the creation of the installation
* and while exporting select that date and export
* then change the date back

`(would've commented but not enough rep)`
If you want to copy pages or sites in between a multisite installation, try the plugin NS Cloner in free version:

1. Install plugin "NS Cloner"
2. My Sites -> Network Admin -> Sites and put mouse over your sit
3. Clone

→ an full copy of a site with all pages is made - in my case it was perfect identical