There are two bromine atoms and one lead atom in the molecule, and they told you that Bromine ions were 1-, therefore the two bromine atoms in the molecule must have had a charge of 1- each, for a total of 2- (2 * 1- = 2-). Therefore the lead atom must have had a charge of 2+, in order to cancel out the 2- of the bromine.
The confusing part (and this confused me too) is that lead is in group four, so has four outer shell electrons, so
should form a 4+ (or 4- or whatever) ion. I looked it up and there's some very complex in depth answer as to why this is
not the case, but I didn't understand it at all and at GCSE level they don't expect us to - they just expected us to look at the 2 x 1- charges of the bromine and figure out that lead must be 2-.
But, this is why the question was ridiculous - I'm sure almost all of us have been taught that a way to figure out what the charge on an ion is is to look at the group number in the periodic table, and this didn't work at all for this question because of reasons that we can't possibly understand at a GCSE level.
I didn't understand this at all until reading through a ton of things earlier, but I managed to get the right answer through misunderstanding the question in a way that happened to be right, which is... good I suppose
TL;DR OCR's question was stupid and everyone was right to be confused