The first large scale electronic computer which became operational in 1946 and contained approximately 18000 vacuum tubes and could perform 300 multiplications per second was known as

The correct answer is B. ENIAC.

ENIAC, or Electronic Numerical Integrator and Computer, was the first large-scale electronic computer. It was built at the University of Pennsylvania’s Moore School of Electrical Engineering and became operational in 1946. ENIAC contained approximately 18,000 vacuum tubes and could perform 300 multiplications per second. It was used to calculate ballistics tables for the U.S. Army during World War II.

The other options are incorrect.

• ILLIAC was an early electronic computer built at the University of Illinois at Urbana-Champaign. It became operational in 1952.
• JOHNIAC was an early electronic computer built at the Ballistic Research Laboratory at Aberdeen Proving Ground, Maryland. It became operational in 1950.
• EDSAC was an early electronic computer built at the University of Cambridge Mathematical Laboratory. It became operational in 1949.

I hope this helps!