Which of the following quantities have three significant figures? 
(a) 3.0066 m                 (b) 0.00309 kg 
(c) 5.05ｘ10⁻²⁷ kg         (d) 301.0 s 
Ans. {(b) and (c)}


Rules for identifying significant figures: 
(i) Non-zero digits are always significant. 
(ii) Zeros between two significant figures are significant. 
(iii) Final or ending zeros on the right in the decimal fractions are significant. 
(iv) Zeros written on the left side of the decimal point for the purpose of spacing the decimal point are not significant. 
(v) In whole numbers that end in one or more zeros without a decimal point are not significant.
The above rules are just for revision, the Answer is start from here

Ans:  

(a) 3.0066 m  
This digit has 5 significant figures

(b) 0.00309 kg 
This digit has 3 significant figures

(c) 5.05ｘ10⁻²⁷ kg  
= 0.00000000000000000000000000505 Kg
This digit has 3 significant figures

(d) 301.0 s   
This digit has 4 significant figures

So, the Correct Answer is {(b) and (c)}


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