In the allene (h2c=c=ch2) molecule:
select one:
a. all the atoms lie in one plane.
b. the ð bonds are delocalised over all three c atoms.
c. the two h atoms on one c lie above and below the plane defined by the other ch2 group.
d. the nonbonding orbitals are full.
e. none of the other options

Option c

Explanation:

In the allene,

Central atom forms two sigma bond and two pi bond.

Hybridization of central atom = sp

Hybridization of two terminal C =

Allene is a nonplanar molecules. This is because of the planes of two groups which are twisted 90 ° to each other.

Therefore, the two H atoms on one C lie above and below the plane defined by the other group.

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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.