Answer:
4 significant figures.
Explanation:
The given measurement have four significant figures 1234.
All non-zero digits are consider significant figures like 1, 2, 3, 4, 5, 6, 7, 8, 9.
Leading zeros are not consider as a significant figures. e.g. 0.03 in this number only one significant figure present which is 3.
Zero between the non zero digits are consider significant like 104 consist of three significant figures.
The zeros at the right side e.g 2400 are also significant. There are four significant figures are present.
Formulas are like steps to solve an equation but in cemistry a formula is 2 or more elements combined to make something
Answer : The volume of 
produced at standard conditions of temperature and pressure is 0.2422 L
Explanation :
Combined gas law is the combination of Boyle's law, Charles's law and Gay-Lussac's law.
The combined gas equation is,
where,
= initial pressure of 
gas = (740-22.4) torr = 717.6 torr
= final pressure of gas at STP= 760 torr
= initial volume of gas = 280 mL
= final volume of gas at STP = ?
= initial temperature of gas = 
= final temperature of gas = 
Now put all the given values in the above equation, we get:
Therefore, the volume of produced at standard conditions of temperature and pressure is 0.2422 L
Answer:
C. 21%oxygen
Explanation:
Dry air contains 78.09% nitrogen, 20.95%oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases.
