If our website is banned by the search engines for black hat practices and if we have corrected our wrong doings we apply for reinclusion.
Manual actions can be taken within Google webmaster tools if you've been penalized.
It means the search engine crawlers would not index the contents and would not follow the links present on the page.
No, Google does not make use of keyword tags.
If you have enough content in the same niche it is better to have it in one big site because first, this way the site is easier to maintain and the great number of pages is good for ranking high in search results. Many small sites allow focusing on specific niches, therefore competing for different keywords.
Google is always trying to work on their algorithm so that "more deserving" websites with better content rank higher than others. The three main algorithm updates of the last two years are Panda, Penguin and Hummingbird.
Nofollow links are not passed by search engines bot and therefore cannot be cached or indexed. Dofollow link is a kind of hyperlink and it passes through all search engines and it puts an impact over page rank.
Verticals means on what themes of websites have you worked so far- this may include education, real estate, IT, travel, Shopping, jobs etc.
Yes, googlebot reads the first 500 KB present in the robots.txt file.
Webmaster tools is a free service by Google from where we can get free Indexing data, backlinks information, crawl errors, search queries, CTR, website malware errors and submit the XML sitemap.
Google has a special format for sitemaps rather than ordinary html format. So it is good to use special XML format that Google uses for sitemaps.