Which one of the following chemicals is a food preservative ?

Consider the following pairs :

Which of the above pairs is/are correctly matched ?

The term 'bitcoin', frequently in the news, is mentioned in the context of :

Circadian rhythm is related to :

Crimean peninsula thrusts into :

 In crustaceans (e.g. shrimp, cray-fish, lobster), the metallic base of the respiratory pigment is :