For how many processes which are sharing common data, the Dekker's algorithm implements mutual exclusion?

ANS:B - 2

Dekker's algorithm is the first known correct solution to the mutual exclusion problem in concurrent programming. The solution is attributed to Dutch mathematician Th. J. Dekker by Edsger W. Dijkstra in his manuscript on cooperating sequential processes. It allows two threads to share a single-use resource without conflict, using only shared memory for communication. It avoids the strict alternation of a naive turn-taking algorithm, and was one of the first mutual exclusion algorithms to be invented. Source: http://en.wikipedia.org/wiki/Dekker's_algorithm