Coals to Newcastle: Needless or superfluous action.

E.g: Why did you bring DVDs with you when I have a home theater? That's like carrying coals to Newcastle.

The correct spellings of the other words are:

Adjourn: to put off, to break off, to postpone something. 

In a sentence: Since the jury could not decide the final decision on the case, the court hearing was adjourned for a week. 

Proceedings: an event or a series of activities involving a set procedure.

Suspicion: a feeling or thought that something is possible, likely, or true.

Discussion: the action or process of talking about something in order to reach a decision or to exchange ideas.

Convenience means 'the state of being able to do something easily with little effort and no hindrances.'

Eg: Electronic appliances have given us a life of convenience.

Veteran means a person who has had long experience in a particular field.

Amateur means a person who engages in a pursuit, especially a sport, on an unpaid rather than a professional basis.

Cosmopolitan means including people from many different countries.

Stoic means a person who can endure pain or hardship without showing their feelings or complaining.

'Convalescent' means recovering from an illness or medical treatment.

So, the most appropriate word for the given group of words is 'Convalescent'.

Let us look into the meaning of other words:

'Altruist' means unselfish regard for or devotion to the welfare of other charitable acts motivated purely by altruism. 

'Senile' means having or showing the weaknesses or diseases of old age, especially a loss of mental faculties.

'Athlete' means a person who is proficient in sports and other forms of physical exercise.

The verb of the sentence can be located in part R which is ‘realised’. From here, one may connect part P and then part Q to form a meaningful and coherent sentence.

The sentence, when brought together, will sound something like this,

The Orientalists could hardly have realised the consequences of their actions.

A preposition is always followed by an object, which is a noun and never a verb. [ subject +verb+ preposition+ object]

It joins a noun, a pronoun, or noun phrases to the rest of the sentence to show their relation.

'into' shows motion. However, in the given sentence, a location is indicated ' a river'.

The correct preposition would be 'in', which indicates 'the location of the action'.

The correct sentence, thus, is: We went for swimming in the river on Sunday.

A plural subject 'girls' needs a plural verb 'talk'.

In the present tense, nouns and verbs form plurals in opposite ways: nouns ADD an S to the singular form; verbs REMOVE the S from the singular form. ex: Singular—the dog chases the cat. Plural—the dogs chase the cat.

As the given sentence is grammatically correct, there are no errors.

The error lies in the first part of the sentence - The trains runs.

A plural subject  'trains' needs a plural verb 'run'.

In the present tense, nouns and verbs form plurals in opposite ways: nouns ADD an S to the singular form; verbs REMOVE the S from the singular form. ex: Singular—the dog chases the cat. Plural—the dogs chase the cat.

The correct part would be to replace' runs' with the plural 'run'.

Thus the correct sentence would be: The trains run on railway tracks which are parallel and never meet.

When one stands, one stands 'by' the side of something. 

On cannot stand 'at' something - one can stand at a location, not something -, one cannot stand 'in' something - unless it is meant to stood in like an amusement ride - and one cannot stand 'beyond' something - one can stand after something, not beyond.