Acatalyst is: a. a solid product of a reaction. b. one of the reactants in a single-replacement reaction. c. not used up in a reaction. d. the product of a combustion reaction.

A catalyst is C. not used up in a reaction.

Explanation:

A catalyst is a substance capable of promoting or accelerating a chemical reaction without directly intervening in it. That is to say that at the end of the reaction the catalyst remains unchanged. Therefore, it is not considered as a reagent or product according to the stoichiometry of the reaction.

Catalysts that are responsible for increasing the speed of a chemical reaction are called positive catalysts and are the most common and used. But there are also  negative catalysts, also known as inhibitory catalysts. These reduce the speed of a reaction.

Catalysts can be classified into:

Finally, the correct answer is a catalyst is not used up in a reaction.

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.

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.