Questions

Polarity :: 

The polarity of a molecule defines its other physical properties such as melting point, boiling point, surface tension, vapor pressure etc... Simply, polarity occurs when the electron distribution in a molecule is asymmetric. This results in a net dipole moment in the molecule. One end of the molecule is charged negative while the other gets a positive charge.

The polarization of a molecule greatly depends on the shape of the molecule. A diatomic molecule like HF mentioned above has no issue of shape. The net dipole moment is only due to the uneven distribution of electrons between the two atoms. However, when there are more than two atoms involved in making a bond, there are many complexities.

The water molecule is of bent shape. Therefore, when the two pair of electrons shared by oxygen with two hydrogen atoms is pulled towards oxygen, the net dipole moment results in the direction of the oxygen atom. There is no other force to cancel out the resultant dipole moment. Hence, the water molecule is highly polar.

Ammonia molecule is of a pyramid shape and the electronegative N atom pulls the electrons towards itself. The three N-H bonds are not in the same plane; hence the dipole moments created do not get canceled out. This makes ammonia a polar molecule.

However, the dipole moments sometimes get canceled due to the shape of the molecules, making the molecule non-polar. Carbon dioxide is such a molecule.

The first attempt in printing was made in England by William Caxton.

William Caxton was an English merchant, diplomat, and writer. He is thought to be the first person to introduce a printing press into England, in 1476, and as a printer was the first English retailer of printed books.

The meanings of the given words are as follows:
Histrionic: excessively theatrical or dramatic in character or style
Melodramatic: characteristic of melodrama, especially in being exaggerated or overemotional
Theatrical: exaggerated and excessively dramatic
Conscientious: wishing to do one's work or duty well and thoroughly
Diligent: having or showing care and conscientiousness in one's work or duties
Tenacious: tending to keep a firm hold of something; clinging or adhering closely
Retentive: (of a person's memory) effective in retaining facts and impressions
Thrive: (of a child, animal, or plant) grow or develop well or vigorously
Tussle: a vigorous struggle or scuffle, typically in order to obtain or achieve something
Pertinent: relevant or applicable to a
particular matter; apposite Appropriate: suitable or proper in the circumstances
Therefore, it can be observed that option  i.e. ‘melodramatic, theatrical’ forms a synonym- synonym pair of ‘histrionic’.

Liquid sodium is being considered as engine coolant.

Members of the House of Representatives serve two-year terms and are considered for reelection every even year.