Uncertainty in Measurement — NEET Chemistry MCQs with Solutions

Solution: Precision refers to how close repeated measurements of the same quantity are to one another (their reproducibility), whereas accuracy refers to how close a measured value is to the true value. For example, readings 1.95 g and 1.93 g are precise (close to each other) but not accurate if the true value is 2.00 g.

Solution: Rule: zeros before the first non-zero digit are not significant, but zeros to the right of the decimal after a non-zero digit are significant. In 0.00340 the leading 0.00 is not counted; the digits 3, 4 and the trailing 0 are significant, giving 3 significant figures.

Solution: To write 0.00048 as N × 10ⁿ with N between 1 and 10, count how many places the decimal point moves right to reach 4.8 — that is 4 places. Each right shift makes the exponent negative, so 0.00048 = 4.8 × 10⁻⁴. Miscounting the shift gives 4.8 × 10⁻³ or 4.8 × 10⁻⁵.

Solution: To write 45600 as N × 10ⁿ with N between 1 and 10, count how many places the decimal point moves left to reach 4.56 — that is 4 places. Each left shift adds 1 to a positive exponent, so 45600 = 4.56 × 10⁴. Miscounting the shift by one gives 4.56 × 10⁵ or 4.56 × 10³.

Solution: Keeping three significant figures means retaining 4, 3, 3 and removing the last digit 6. Since the digit to be removed (6) is greater than 5, the preceding digit is increased by one: 3 becomes 4. Hence 4.336 rounds to 4.34.

Solution: In addition, the result cannot have more digits after the decimal point than the number with the fewest. 3.24 + 0.2 = 3.44, but 0.2 has only one digit after the decimal, so the answer is reported to one decimal place: 3.4.

Solution: By the unit-factor method, 8 in × (2.54 cm ÷ 1 in) = 8 × 2.54 = 20.32 cm; the inch unit cancels. Dividing (8 ÷ 2.54) gives the wrong 3.15 cm and adding (8 + 2.54) gives 10.54 cm.