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An IR band near 1715 cm⁻¹ is characteristic of a saturated aliphatic ketone C=O. The molecular formula C4H8OC_4H_8O also fits a ketone (degree of unsaturation = 1). The 1^{1}H NMR pattern—singlet at ~2.1 ppm (3H) for a methyl directly attached to a carbonyl (–COCH₃), quartet at ~2.4 ppm (2H) for a methylene adjacent to the carbonyl (–COCH₂–), and triplet at ~1.0 ppm (3H) for a terminal methyl (–CH₂CH₃)—matches 2-butanone precisely. Option A (1-butanal) would typically show an aldehydic proton near ~9–10 ppm, absent here, and an IR aldehyde C–H stretch around 2720–2820 cm⁻¹. Option C lacks a carbonyl (IR mismatch) and would show a broad O–H stretch ~3300 cm⁻¹. Option D (alkene) would shift IR to ~1650 cm⁻¹ and show vinyl protons ~4.5–6.5 ppm. This question integrates spectral interpretation—an important DAT organic skill linking IR and NMR fingerprints to consistent structures.

Acid (HCl) + base (NaOH) → salt (NaCl) + water is a neutralization reaction, a subtype of double replacement. Combustion involves oxygen, decomposition breaks one compound, and redox requires electron transfer. DAT chemistry often features acid–base reactions.

Annual depreciation = 10% of 10,000 = $1,000. After 3 years: 10,000 − 3,000 = $7,000. Option A is correct. DAT QR depreciation problems require distinguishing fixed depreciation vs percentage of remaining value.

s orbitals are spherically symmetric around the nucleus. p orbitals (B) are dumbbell-shaped, d orbitals (C) often clover-shaped, and f orbitals (D) more complex. Shape relates to angular momentum quantum number (l): l=0 (spherical), l=1 (p), l=2 (d), l=3 (f). DAT general chemistry often tests orbital shapes and quantum numbers.

The passage explicitly mentions inhibition of bacterial metabolism. This decreases acid production and lowers caries risk. A, C, and D contradict the stated effect. DAT RC requires careful matching with passage evidence.