Workers in the formal sector typically have jobs that are regular, structured, and come with certain employment benefits and legal protections.

Among the options provided:

1. B. A clerk in the electricity office is most likely considered to be working in the formal sector. Office jobs, especially in government or established private sector organizations, are typically part of the formal sector.
2.  C. A police constable is also generally considered to be working in the formal sector. This profession is associated with government employment and is characterized by a formal employment structure.
3. E. A nurse in a government hospital can be considered as working in the formal sector. Government jobs, including those in healthcare, are typically part of the formal sector.

So, the correct answer is:

2. B, C, and E only.