Generally speaking irregardless of whether you only applied for the mobility element I think they will probably assess you on all of it.
If you look at the form, basically they will ask you questions regarding each descriptior (so for the care part: can you cook a meal unaided? Do you ever help to take nutrition? Can you manage your medication/treatment? Can you cope with washing/bathing? Can you cope socially around other people, can you manage money etc).
The mobility part is really only 2 questions,
Can you navigate an unfamiliar journey unaided and can you walk more than 20 meters etc.
They won't necessarily ask you direct questions. They may ask if you can drive. They ask this, despite it not technically being relevant because what they do is for example use the fact you can drive to say that that you have sufficient concentration/navigation/cognition etc. they might ask if you have a pet. If you do they may from that decide you have no issues remembering to feed or walk them. And if you work, whilst working is 100% not a barrier to claiming PiP does your job contradict what you say you can't do? (Often having a job is a reason they use to justify to have sufficient motivation to eat/bathe etc).
That sounds like I'm saying they are trying to "catch you out" it's not that per say but be aware that the questions they ask may seem irrelevant but they are in fact relevent to them.
My advice, dont lie. And please for the live of god do not take the often offered bad advice of describing everyday as your "worst day" (unless everyday literally is a worst day). If it's a fluctuating condition give them the full picture, good/bad and average days. To be eligible you must have the needs more than 50% of the time to be eligible.
Submit as much evidence as possible. Any medical reports that reference your daily living/mobility/restrictions especially as that will give you a stronger case.