Which of these equations does not represent an oxidation-reduction reaction?

a. 3Al + 6HCl → 3H2 + AlCl3

b. 2H2O → 2H2 + O2

c. 2NaCl + Pb(NO3)2 → PbCl2 + 3NaNO3

d. 2NaI + Br2 → 2NaBr + I2

c. 2NaCl + Pb(NO3)2 → PbCl2 + 3NaNO3

Explanation:

In the others the elements change their oxidation number when they convert in products. In this reaction no.

Reagents

NaCl= Na (+1),Cl(-1)

PB(NO3)2= Pb(+2), N(+5), O(-2)

Products

PbCl2= Pb(+2), Cl(-1)

NaNO3= Na(+1), N(+5), O(-2)

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.

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.