An electrically neutral atom of gallium has 31 electrons and 39 neutrons. what is the mass number for an atom of gallium? . a. 31. b. 35. c. 62. d. 70

Option (D) is the correct answer.

Explanation:

Mass number is the sum of total number of protons and neutrons present in the nucleus of an atom.

On the other hand, atomic number is only the total number of protons present  in an atom.

Also, when an atom is electrically neutral in nature then its number of protons equal to the number of electrons present in it.

For example, an electrically neutral atom of gallium has 31 electrons and 39 neutrons. This means that it also contains 31 protons.

Hence, mass number of gallium will be as follows.

                Mass number = no. of protons + no. of neutrons

                                        = 31 + 39

                                        = 70

Thus, we can conclude that the mass number for an atom of gallium is 70.

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.