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I think it should be option a)

All query $1,3,4$ are equivalent but $2$ is not equivalent.

Query $2$ should be 

$\prod \text{Room no,hotel no,type,price}(\sigma \text{type='single' } \wedge \text{price=200 })$

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Why? query 2 is also equivalent. It will print all rows of data with condition given.
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1 Answer

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When you don't use project and do only select, by default all the columns are returned, thus making Query 2 same as Query 1. 

Eg:

by

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can u refer any link for that ? @goxul
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@arvin Sure, here you go. http://infolab.stanford.edu/~ullman/fcdb/aut07/slides/ra.pdf

From Jeffrey Ullman's DBMS slides.

You can find all of them here: http://infolab.stanford.edu/~ullman/fcdb/aut07/

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thanks bro :)
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