L-2 SIGNIFICANT FIGURES || SOME BASIC CONCEPTS OF CHEMISTRY || JEE MAINS || NEET CBSE ICSE BOARDS

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Significant Figures Sig Figs
Definition:
Significant figures are the digits in a number that carry meaning about its precision.
They include:
✔ All non-zero digits
✔ Zeros between non-zero digits
✔ Trailing zeros after decimal
✔ Leading zeros never significant
⭐ Rules for Counting Significant Figures
1. All non-zero digits are significant
Example:
345 → 3 sf
71.9 → 3 sf
2. Zeros between non-zero digits are significant
Example:
105 → 3 sf
1008 → 4 sf
3. Leading zeros are not significant
(These zeros only show the position of decimal)
Examples:
0.05 → 1 sf
0.00720 → 3 sf
0.000402 → 3 sf
4. Trailing zeros in a number with a decimal are significant
Examples:
20.0 → 3 sf
0.500 → 3 sf
48.700 → 5 sf
5. Trailing zeros without a decimal are not significant
Examples:
200 → 1 sf
3000 → 1 sf
2500 → 2 sf
6. Exact numbers have infinite significant figures
Examples:
100 students (counting)
12 eggs in a dozen
Conversion factors: 1 m = 100 cm → ∞ sf
⭐ Rules for Calculations
A. Multiplication & Division
The final answer should have the same number of significant figures as the number with the least significant figures.
Example:
4.62 × 3.1
Least sf = 2
Answer = 14 (2 sf)
B. Addition & Subtraction
The final answer should have same number of decimal places as the number with the least decimal places.
Example:
12.11
3.2
= 15.31 → round to 15.3
⭐ Rounding Rules (Very Important)
If the digit to be removed is 5 → leave previous digit unchanged.
If it is 5 → increase previous digit by 1.
If it is exactly 5 →
If previous digit is even, leave it (even rule).
If previous digit is odd, add +1.