ANSWERS

1.   I am sleeping because I am alert.  

        Viruddha hetu (Self-contradicting reason)       
        Being alert and sleeping  are self-contradicting

 
2.   Castor oil is sweet because it is a liquid like water.

        Badhitha hetu (contradicting reason)
        By physically tasting castor oil we can conclude that it is not sweet.

           
3.   Lemon has sour taste because  it is yellow in colour.           

        Sadharana savyabhichara hetu (Common straying)
        Even banana is yellow in colour which is not sour to taste

 
4.   Humans have sixth sense because they have  46 chromosomes.

        Asadharana savyabhichara hetu ( Uncommon straying )
        No other animal other than humans have 46 chromosomes. So there are no similar or  contrary instances.

5.   Glucose tastes sweet because it is white in colour like sugar 

        Satpratipaksa hetu (Antithetical reasoning)
        Glucose doesn't taste sweet because it is amorphorous like talcum powder .

6.   Man has life because he is eternal        

        Svarupasiddha  ( Unestablished in respect of itself).
        Man is not eternal.

7.   Pure water has a very good smell because it is a liquid like eucalyptus oil.

        Badhitha hetu (Contradicting reason)
        One can smell pure water and conclude that it is odourless.                   

8.   Man can move because he has life like any other animal.

        Sadharana savyabhichara hetu (Common straying ).
        Even plants have life which cannot move.

                    
9.   Tigers in Moon  are carnivorous like tigers in Earth.

        Asrayasiddha ( Unestablished in respect of its substratum)     
        There are no tigers in moon.              

           
10.   Orange is spherical, because it is a fruit like lemon.

         Sadharana savyabhichara hetu (Common straying)        
    Banana, which is also a fruit is not spherical.          

11.    Diamond is costly because it is  a gem like sapphire. 

         Satpratipaksa hetu (Antithetical reasoning).
Diamonds are cheap because it has carbon as  coal

12.    Birds can fly because they can vary their body size. 

         Svarupasiddha (Unestablished in respect of itself ).
         Birds cannot vary their size.     So the hetu doesn't exist in  paksha.