The number of significant figures in the numbers 5005, 500.0, and 126,000 are, respectively: 
1. 2, 4, and 3 
2. 4, 1, and 3 
3. 4, 4, and 6 
4. 4, 4, and 3 

What is the difference between 0.50 mol Na₂CO₃ and 0.50 M Na₂CO₃?

Round up the following numbers into three significant figures: 
(i) 10.4107 
(ii) 0.04597

The following data was obtained when dinitrogen and dioxygen react together to form different compounds:

The law of chemical combination applicable to the above experimental data is:
1. Law of reciprocal proportions
2. Law of multiple proportions
3. Law of constant composition
4. None of the above.

Which of the following correctly represents 234,000 and 6.0012 in scientific notation?

How many grams of HCl are required to react with 5.0 g of manganese dioxide in the reaction provided?
\(4 \mathrm{HCl}_{(\mathrm{aq})}+\mathrm{MnO}_{2(\mathrm{~s})} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}+\mathrm{MnCl}_{2(\mathrm{aq})}+\mathrm{Cl}_{2(\mathrm{~g})}\)

1. 4.8 g

2. 6.4 g

3. 2.8 g

4. 8.4 g

Find the mass of CaCO₃ required to completely react with 25 mL of 0.75 M HCl according to the reaction:

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l)

1. 0.36 g

2. 0.09 g

3. 0.96 g

4. 0.66 g

Burning a small sample of welding gas (constituted of C and H only)  in oxygen gives 3.38 g carbon dioxide, 0.690 g of water, and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Molecular formula of welding gas would be:

1. C₂H₂

2. C₂H₆

3. CH

4. C₂H₄

Which of the following contains the highest number of atoms?

1. 52 moles of Ar

2. 52 u of He

3. 52 g of He

4. All of the above have the same number of atoms