Acombustion reaction involves the reaction of a substance with oxygen gas. the complete combustion of any hydrocarbon (binary compound of carbon and hydrogen) produces carbon dioxide and water as the only products. octane is a hydrocarbon that is found in gasoline. complete combustion of octane produces 8 l of carbon dioxide for every 9 l of water vapor (both measured at the same temperature and pressure). what is the ratio of carbon atoms to hydrogen atoms in a molecule of octane?

Explanation:

First, we need to write the balanced equation of the combustion of octane, which is an alkane (has only hydrogen and carbons and saturated bonds), that has molecular formula CnH2n, so for n = 8: C₈H₁₈.

C₈H₁₈ + (25/2)O₂ → 8CO₂ + 9H₂O

Because of the pressure and temperature remains constant, volume is equal to the number of atoms. So, carbon dioxide has 1 atom of C, and water has two atoms of H, then:

It's proven by the molecular formula of octane showed above.

specific gravity is the density of a substance divided by the density of water. since (at standard temperature and pressure) water has a density of 1 gram/cm3, and since all of the units cancel, specific gravity is usually very close to the same value as density

so "c" is the answer

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a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.