Sumant,  You can use dynamic values in the query using the ":" notation; however, in your example, you need specific combinations of two fields.  So the following will give you more results than you want:

Set<String> months = new Set<String>
{   'January', 'February', 'March', 'April', 'May', 'June',
    'July', 'August', 'September', 'October', 'November', 'December'
};
Set<String> years = new Set<String>{ '2016', '2017' };

List<My_Object__c> records =
(   [   SELECT  Id
        FROM    My_Object__c
        WHERE   (YEAR__c IN :years AND Month__c IN months) OR YEAR__c = null
    ]
);

To get around this problem, you can add a string formula field (Month_Year__c) to your object that concatenates the month and year:

Month__c + ", " + YEAR__c

Then your query can look like this:

Set<String> monthYears = new Set<String>
{   'July, 2016', 'August, 2016', 'September, 2016', 'October, 2016',
    'November, 2016', 'December, 2016', 'January, 2017', 'February, 2017',
    'March, 2017', 'April, 2017', 'May, 2017', 'June, 2017'
};

List<My_Object__c> records =
(   [   SELECT  Id
        FROM    My_Object__c
        WHERE   Month_Year__c IN :monthYears
    ]
);

You might even come up with a way to dynamically generate the set.

On the other hand, you could define the Month_Year__c field as a date formula:

DATE(
  VALUE( YEAR__c ),
  CASE( Month__c,
    "January", 1,
    "February", 2,
    "March", 3,
    "April", 4,
    "May", 5,
    "June", 6,
    "July", 7,
    "August", 8,
    "September", 9,
    "October", 10,
    "November", 11,
    "December", 12,
    0
  ),
  1
)

And then you can use the SOQL date operators:

Date startDate = Date.newInstance( 2016, 7, 1 );
Date endDate = Date.newInstance( 2017, 6, 1 );

List<My_Object__c> records =
(   [   SELECT  Id
        FROM    My_Object__c
        WHERE   (   Month_Year__c >= :startDate
                AND Month_Year__c <= :endDate
                )
    ]
);

Let me know if you have any questions.