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PCC is a mild oxidizing agent that converts primary alcohols to aldehydes without over-oxidizing to carboxylic acids. Stronger oxidants (KMnO₄, CrO₃) yield carboxylic acids. Secondary alcohols oxidize to ketones, while alkanes (D) are unrelated. DAT organic frequently tests reagent selectivity.

Let x = original. After 20% decrease: 0.80x = 80 → x = 80 ÷ 0.80 = 100. Correct answer = C. Careful: Option D miscalculates. DAT QR requires setting up decrease equations as (1 − r) × original.

The passage highlights slow, sustained fluoride release as the protective mechanism. Other options are unrelated or incorrect. DAT RC answers must follow passage details.

Ammonia (NH₃) consists of a central nitrogen bonded to three hydrogens and containing one lone pair. That gives four electron domains around nitrogen, which corresponds to sp³ hybridization. The electron geometry is tetrahedral, while the molecular geometry is trigonal pyramidal due to lone pair repulsion. Option A (sp) would be for linear arrangements such as in acetylene (C₂H₂). Option B (sp²) describes trigonal planar arrangements like in BF₃ or alkenes. Option D (dsp³) corresponds to trigonal bipyramidal arrangements (e.g., PCl₅). On the DAT, quickly applying VSEPR and electron domain counting leads to the correct hybridization assignment. Remember: lone pairs are counted as electron domains even if not directly visible in bonding.

Each hygienist works 6 h−0.5 h=5.5 h=3306\text{ h} - 0.5\text{ h} = 5.5\text{ h} = 330 minutes of appointment time. With 45-minute slots, the number of whole appointments per hygienist is ⌊330/45⌋=7\lfloor 330/45 \rfloor = 7. Across 3 hygienists, total scheduled = 3×7=213 \times 7 = 21. With a 15% no-show rate, expected seen = 0.85×21=17.85≈180.85 \times 21 = 17.85 \approx 18. Option D (21) ignores no-shows; Option C (19) reflects rounding the expected value up, but in expectation problems, standard practice is to round to the nearest whole number unless instructed otherwise—18 is closest. Option A underestimates by double-counting breaks or misapplying the percentage. For QR on the DAT, translate operational constraints into time slots, compute an integer capacity, and then apply percentages to the total—not to each hygienist separately—to avoid compounding rounding errors.