The amount of energy released from a fission reaction is much greater than the energy released from a chemical reaction because in a fission reaction
(1) mass is converted into energy
(2) energy is converted into mass
(3) ionic bonds are broken
(4) covalent bonds are broken

Mass is converted into energy.

Explanation:  There are mainly 2 types of nuclear reactions -

a) Nuclear Fission - in which one heavy nucleus gets break into two or more products releasing tremendous amount of energy especially kinetic energy. The amount of energy released due to mass-energy equivalence principle is higher as some amount of mass of the nucleus gets converted into the energy thus decreasing the mass.

The image of the reaction is attached.

b) Nuclear Fusion - in which 2 or more nuclei fused together to form a heavy nucleus  .

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.

it would be b. 6co2 + 6h2o --> c6h12o6 + 6o2