UCL Pharmacology with B in chemistry?

UK unis actually on the whole aren't really that fussed about random extracurriculars like volunteers or similar. They care much more about specifically relevant stuff you've done for the course like wider reading. The except is for healthcare professions courses which often have work experience (including voluntary work) requirements. Note that pharmacology is not a healthcare professions course, it's a science degree.
I suspect though not meeting the chemistry grade is going to make you non-competitive for it, maybe unless you are a contextual applicant? Even then it's probably considered minimum required background knowledge to succeed on the course. Of course, equally, you have 5 whole options and can only accept offers from two at most, so there's not a great deal of risk in rolling the dice with UCL if you have picked suitable options for your other choices

I'm in the exact same position as you except these grades are my predicted not achieved. From looking at the website, it doesnt specifically say an A in chem, just that chem is required so I'm pretty sure you meet the entry requirements.

The thing is if I couldnt get into UCL I would probably want a different course like an engineering foundation year. I guess the decision is whether to fit my whole application for a shot at UCL and then to have a backup uni that would be OKAY