In the RSA public key cryptosystem, which one of the following numbers will always be largesta.qb.nc.pd.e

The question seems to be incomplete. The options (a.q, b.n, c.p, d.e) are not clearly defined in the context of RSA public key cryptosystem.

However, in the RSA algorithm, typically the public key (n) is the largest number. The public key consists of the number n, which is the product of two large prime numbers (also known as the modulus), and the number e (known as the public exponent).

The private key consists of the number n (the same modulus as used in the public key) and the number d (known as the private exponent).

The number q is typically one of the two prime numbers used to create the modulus n.

So, without additional context, the answer would be b.n, as n is the product of two prime numbers and is typically the largest number in the RSA public key cryptosystem.

Please provide more context or clarify the question for a more accurate answer.