Which letter cluster will replace the question mark (?)

Which of the following gases in air is responsible for the discoloration of Brass?

Who was appointed as the 52nd Chief Justice of India (CJI)? 

In which foreign banks can the Reserve Bank of India ( RBI ) keep its forex reserve gold?

1 ) Bank of England

Mahmud Begda was a famous sultan of which famous empire?

What medical device is used to measure blood pressure? 

Exercise ‘SADA TANSEEQ’ is conducted between which two countries?

Where did NMDC Limited and MECON Limited inaugurate their international offices to expand India’s industrial presence?

When did the Constitution of WHO come into force - a date which we now celebrate as World Health Day every year?

Which of the following statements about "Truck farming' is/are correct?

Kirsty Coventry, who became the first female and first African President of the International Olympic Committee (IOC) in 2025, belongs to which country?