Although digital platforms raise a host of complicated issues, the government has a ______ to protect its citizens-as it already does in other, equally complex areas. 1. rigmarole 2. strife 3. duty 4. pledge 5. responsibility 6. stake

We need a noun here as denoted by the use of the article A (articles are used to modify only nouns). The sentence seeks to convey that the government has to address the concerns of the citizens by addressing the issues related to digital platforms. DUTY and RESPONSIBILITY fit contextually. If you have RESPONSIBILITY for something or someone, or if they are your responsibility, it is your job or duty to deal with them and to take decisions relating to them. RIGMAROLE- a lengthy process STRIFE- angry or bitter disagreement over fundamental issues; conflict. PLEDGE- a solemn promise or undertaking. STAKE- a share or interest in a business, situation, or system.