NG900
a. Poorly written, no units specified (VCAA almost always specifies units) but if it's asking for molar concentrations just interpolate from line of best fit as I've described. Usually if they don't mention units it's assumed to be the same units as the one they gave you in the question ie M
b. Yet another absolutely rubbish question. When I converted M which looks to be about 0.10 M interpolating from the absorbance into g/L by multiplying by the molar mass of P (31 g/mol) and divided this by 4 (to account for 250 mL volume), it's saying I have 0.775 g of P in only 0.250 g of the detergent which fails a sanity check. Note here you can assume [PO4 3-] = [P] since there's 1 P atom per phosphate and we're only interested in P atom mass. I think whatever dodgy website you've gotten this from or the textbook must've messed up the axes labelling since my working steps must be correct as mol/L x g/mol = g/L by dimensional analysis. Either way I'm not surprised, I've seen so many typos in textbooks that I can safely say that their qualities are on par with the many random websites out there with incorrect solutions to practice problems
c. Remember your factors for wavelength selection, maximum absorption to optimise sensitivity and a small dA/d(wavelength) around the turning point (if it absorbs a super specific wavelength ie the gradient on either side of the turning point is too steep then when you measure absorbance you might get readings that have poor absorbance since they were slightly off the turning point
