[RahulK]

Given answer is a),

but I believe its b)

any comments

When you read the below wiki link for : Specific techniques / Gram staining

https://en.wikipedia.org/wiki/Staining

The Gram negative bacteria has outer lps layer. 
Thus the gram negative bacteria is able to hold the secondary stain (safranin stain).

Same has been said by few others in the below link as well:

https://www.quora.com/Is-safranin-necess...-If-so-why