Q.(a)

(i) The vinegar acid's empirical formula works out to CH2O from its percentage composition. (ii) The spin quantum number (+1/2 or -1/2) describes an electron's intrinsic spin direction and underlies the Pauli exclusion principle.

Answering part (a), since (a)(i) and (a)(ii) are given as the primary alternative (the OR alternative (b), on similarities between beryllium and aluminium, is not required unless (a) is unanswerable):

(a)(i) Empirical formula from percentage composition (40% C, 6.6% H, 53.4% O):

Step 1 — Moles of each element (using 100 g of compound as the basis, so grams = percentages):

Moles of C = 40 / 12 = 3.333

Moles of H = 6.6 / 1 = 6.6

Moles of O = 53.4 / 16 = 3.3375

Step 2 — Divide each by the smallest value (3.333) to get simplest whole-number mole ratio:

C: 3.333 / 3.333 = 1.0

H: 6.6 / 3.333 = 1.98 (approx 2)

O: 3.3375 / 3.333 = 1.001 (approx 1)

Step 3 — Simplest whole-number ratio C : H : O = 1 : 2 : 1

Empirical formula = CH2O

(This matches acetic acid, CH3COOH, the acid present in vinegar, whose molecular formula C2H4O2 is exactly twice the empirical formula CH2O.)

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