B.Sc Eligibility

Yes, you can take this branch if you had PCM in 12th.

Yes, you can get admission in B.Sc chemistry after completing your Diploma. But, why don't you opt for B.Sc chemistry directly?

Hello, yes you can take GRE after B.Sc., it is usually taken after a Bachelors degree to pursue Masters degree majorly in US and Canada. There is no eligibility criteria on the whole.
Why don't you check: ets.org/gre, this is the official GRE website.

Please refer to http://www.tmv.edu.in/msps_mas_mastermassmedia.asp. You are eligible for MA in Mass Communication based on your graduation degree qualification.

Hi Jay, the minimum requirements to apply to UVic - Graduation from a recognized high school with either the All India Senior School Certificate (CBSE) or the Indian School Certificate (awarded by the CISCE) with 70%. I believe you have a score of 68% so not quite eligible. Write to the university before applying.
To pursue BS degree you must complete 12 years of formal education. There is no age limit but if applicants do have gaps they must provide supporting statements.
I will advice you contact directly with the universities.

Hi Jay, do you mean BS in Computer Science?
Eligibility criteria will vary slightly with the universities. Mostly good academic grades during 10+2 and strong mathematical foundation is required. A grade above 70% to 75% is recommended for the top universities. Additionally you must take IELTS or TOEFL. A good score generally is 6.5 in IELTS or 100 in TOEFL. You must visit the university websites for IELTS or TOEFL requirements. Hope it helped.

Please check with the university.