I am currently planning to use someone's tweet in my book & tweet won't include any images (which will made commercially available). So , first are tweets intellectual property protected by certain copyright laws and if so will I be sued if I use it in my book even if I give reference to whose tweet it was ???
It's hard to say, under the Twitter TOS. They do not claim that copyright is transfered to them: "You retain your rights to any Content you submit, post or display on or through the Services. What’s yours is yours — you own your Content (and your photos and videos are part of the Content)". But you do license the content:
By submitting, posting or displaying Content on or through the Services, you grant us a worldwide, non-exclusive, royalty-free license (with the right to sublicense) to use, copy, reproduce, process, adapt, modify, publish, transmit, display and distribute such Content in any and all media or distribution methods (now known or later developed). This license authorizes us to make your Content available to the rest of the world and to let others do the same. You agree that this license includes the right for Twitter to provide, promote, and improve the Services and to make Content submitted to or through the Services available to other companies, organizations or individuals for the syndication, broadcast, distribution, promotion or publication of such Content on other media and services, subject to our terms and conditions for such Content use. Such additional uses by Twitter, or other companies, organizations or individuals, may be made with no compensation paid to you with respect to the Content that you submit, post, transmit or otherwise make available through the Services.
The totality of conditions, including the Twitter Rules, is ever-evolving and not apparently contained in a single link. From what I can tell, there is no condition that prohibits a user from copying tweets into a book. There are numerous statements about "respecting copyright" which refer to taking material that is not licensed to Twitter and redistributing: nothing about redistributing licensed material.A plain reading of the first bold sentence says that you can make your content available to the world, not restricted to "retweeting".
A tweet is intellectual property, protected by copyright law. I haven't read the Twitter terms of service, but I'd assume that the copyright is held by the user with permission for Twitter to reuse it.
It sounds like you're talking about quoting a single tweet to illustrate something in a full book about something else. If that's the case, I'd expect your tweet to be protected as a fair use -- similar to when the New York Times embeds a Donald Trump tweet in a news story. If your book is nothing more than a collection of tweets, that's a tougher call.
Of course, the question of whether you'll be sued cannot be answered. But if you are, it sounds like you'd have a strong defense.