Yes, admission to engineering without giving an entrance exam is possible on the basis of 12th marks. The admission process varies from college to college and the criteria depend on the policies of the institution. Here are some ways to secure admission in engineering without giving the entrance exam:

1. Direct Admission through Management Quota:
Many private engineering colleges offer direct admission through management quota seats. These seats are reserved for students who are willing to pay a higher fee. The admission criteria for management quota seats are generally based on the student's 12th percentage.

2. State Quota:
In many states, engineering colleges reserve a certain percentage of seats for students who have domicile in that state. The admission criteria for state quota seats are generally based on the student's 12th percentage.

3. Merit-Based Admission:
Some private engineering colleges offer merit-based admission to students who have scored a high percentage in their 12th examination. These colleges generally have a cut-off percentage, and students who meet the cut-off criteria are eligible for admission.

4. Lateral Entry:
Students who have completed a diploma in engineering can apply for lateral entry admission to the second year of the engineering course. The admission criteria for lateral entry are generally based on the student's diploma percentage.

In conclusion, admission to engineering without an entrance exam is possible on the basis of 12th marks. Students can apply through management quota, state quota, merit-based admission, or lateral entry. However, it is important to note that the admission criteria vary from college to college, and students must research the policies of the institution before applying.