This is a question from SL Arora, so don't bash me. My initial thoughts were "Number of Field lines? well it should be infinity, You can draw how much ever field lines you want" However the author went on to say
Number of lines of force originating from a charge of 1 Coulomb = Electric flux through a closed surface enclosing the charge.
And so the author used the concept of flux to the number of field lines originating. The concept of flux is indeed related to the number of field lines passing through the surface.
But Flux is defined as "the total electric or magnetic field passing through a surface." It does NOT however tell us the number of field lines originating from the proton. At the end of the day, Flux is directly proportional to the number of field lines crossing through a surface, not equal to it. I think this is where Arora got it wrong
Interestingly, I remember stumbling upon a question from HC Verma telling
In some old texts, it is mentioned that 4$\pi$ lines of force originate from each unit positive charge. Comment on the statement in the view of the fact that 4$\pi$ is not an integar
However unlike SLA, HC Verma didn't bother giving the answer, so I can't tell what the answer is in his opinion
So what exactly is the consensus on the number of Line of force emerging from a unit positive charge
Edit1: I pulled out all dodgy citations and decided to simply compare what is given by the two books with regards to the line of force originating from a positive charge. Also, I will now use the terms "Line of force" and "Electric fieldlines interchangeably" unless someone objects
Edit2: I also went into whether flux can actually give you the number of fieldlines and came to conclusion, (1) NO IT CANT (2) most importantly the Question could be incorrect then