Questions

There are 60 minutes in an hour.

In ¾ of an hour there are (60 × ¾) minutes = 45 minutes.

In ¾ of an hour there are (60 × 45) seconds = 2700 seconds.

Siren sounds for every 5 seconds.

In 2700 seconds = 2700/5 = 540 times.

The count start after the first sound, the Siren will sound 541 times in ¾ of an hour.

IUPAC stands for International Union of Pure and Applied Chemistry.

A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC).

The GVK group-run Mumbai airport has become the world’s busiest amongst the single-runway facilities by handling 837 flights a day or one in 65 seconds on an average in fiscal 2017.

"Pure Banking, Nothing Else" - is a slogan raised by SBI -  State Bank of India.

The other answers could be accurate in specific situations, but their role alone does not meet the keyb criterion of being "external" to the project team. Answers A, B, and D are incorrect because these individuals are not external to the project.