Can I get a better job option in Merchant Navy after passing 12th grade examination

Yes you can join Merchant Navy after passing 12th grade examination.. to join merchant navy you have to pass one of the following courses .

3 month Pre-Sea Course in Deck rating.
3 month Pre-Sea Course in Engine rating.
4 month Pre-Sea Course in Saloon rating.
STCW Course
1 year Pre-Sea Diploma in Nautical Science
HND (Higher National Diploma) Nautical Science
B.E Marine Engineering (4-Year Degree course in Marine Engineering)

Eligibility
The applicant should have completed 12th std. with PCM from Recognized board of India.

Age limit:
Age of Candidate should not exist 21 years

Physical requirements:
Eye Sight = 6/6,
Height = 167 cms,
Weight = 50 Kg
Chest = 77 cm (Normal) / 82 cm (Expanding)

The selection in Merchant Navy will be on the basis of following:
Written Examination
Medical Examination