In formal American English, the correct version of the question is:
c) Are X and Y the exact same thing?
The subject and verb are plural, because we start by discussing two different concepts.
The complement is singular -- one hypothetical concept that the subjects might be identical to.
An equally correct question is:
d) Are X and Y two different things?
In this question, the complement is plural.
In English, 'pasta' is not usually a plural noun, it is a mass noun (or 'uncountable' noun). Arguably, you could refer to different kinds of pasta as "pastas" (although most English speakers would not), but if referring to pasta as one substance it is just "pasta".
The advert you are referring to is not saying that different kinds of pasta are the same - they are clearly not. Farfalle, penne, spaghetti, are all different in shape if nothing else.
The advert is clearly talking about the quality of pasta as a substance, saying that not all brands of pasta are the same, and suggesting that the one being advertised is superior.
Note that this applies to English and may well be different from some Latin languages - the term 'spaghetti', for example, is a Latin plural form (just as 'cacti' is the plural of cactus) and technically one single strand of spaghetti should be known as a 'spaghetto'; however, this is unknown to the majority of native English speakers and we just don't use that term. Additionally, don't take this as a rule for all Latin languages - for example, neither Italian nor French uses 'cacti' as the plural for cactus.
Best Answer
The first sentence is correct as although "father's grandfather" and "grandfather's father" are referring to the same person but at the time of speaking/referring, they are the instances of a singleton personality.
Further, the grandfather's father instance is older than father's grandfather( considering the natural timeline). Thus, due to different instances of the same person for two different perspectives, "is" can't be used in this context.