Which period contains elements that are all gases at stp

Period 1

Explanation:

Periods are the horizontal rows in the periodic table. They contain elements with the same number of electron shells. Period 1 has just two elements which are hydrogen (H) and helium (He). These two elements are gases at stp.

Hydrogen is a diatomic element that exist as gas at STP while helium is a monoatomic element that exist as a gas at STP. Hydrogen is found in group 1 and period 1 of the periodic table. Helium is found in the group zero of the periodic table - elements in group zero are called noble/rare/inert gases. Though, helium has just two electrons, its two electrons however completely fill its one and outermost shell which makes it "eligible" to be in the group zero.      

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.