Solution:
No article is required.

Solution:
Here, a specific epic poem 'Ramayana' is being talked about. 'The' article will be used.

Solution:
We are not referring to a specific coat. Hence, we need to use an indefinite article. Since 'coat' begins with a consonant sound, the article 'a' is the answer.

Solution:
No article is required.

Solution:
"The" is a definite article which is used before a noun that is fixed, special or discussed earlier. "A/An" is used before an indefinite singular noun. "Union leader" is a fixed noun. Hence "the" will be used.

Solution:
Use 'an' before words such as "hour" which sound like they start with a vowel even if the first letter is a consonant. Also use 'an' before letters and numbers which sound like they begin with a vowel, such as "F" or "8". 'An' will be used before 'sms'.

Solution:
'Blue one' indicates specificity about a particular shirt. Hence, definite article 'the' will be used.