Now let see how many adsense unit ads allowed and can place in a page ! Adsense is such a fantastic option for publishers who have sufficient traffic in their website. There are more CPC sites to publish their ad units. But adsense is unique and it has fantastic features. You can go and search about adsense exactly at adsense.google.com
Adsense ads placements in a webpage
1. You can add 3 adsense for content ads like text, image or rich media ad units in a webpage maximum. (Verified)
2. Same as before you can add 3 horizontal or vertical link units maximum in a webpage. (Verified)
3. Search box is little different. Only you can add 2 adsense custom search boxes in a webpage. If you add search box with Google's logo mean, its quite good. (Verified)
4. Hope you know, Adsense's video link ad has been aborted. (Verified)
Related adsense tips
Do not edit like length and width in adsense script code. Simply, do not edit even single word of adsense code. Because it will consider as violation of adsense and your adsense account may be permanently blocked. Now a days opening new adsense account is very hard than before.
If you getting good traffic with unique content mean, adsense will approve your account without fail, else your account will get disapproved. So that telling, try to remain in safe place to keep your previous adsense account. So keep concentrate on placing ad units in your webpage promptly. Google's adsense will allow to place your ad units only in webpages, not in emails, newletters, softwares or insisting to pay per click programs.
Hope you understand what i am coming to say about adsense's violations and ad units. Apply this formula and get succeeded !