Income tax -gratuity fund trust/saf trust etc.

A query:

Many Big Companies establish Gratuity Trust, Superannuation Trust, PF Trust etc for their employees and maintain separate records & Books for that. Also Contribution from Employers & Employees are transferred to these Trusts & those Contributions are invested in some outside market for Additional earnings. 

Are these Trusts are Approved Gratuity Fund, Approved Superannuation Fund etc. as defined in the Income Tax?

Contribution made by Companies are allowed as deductions?

How these are Trusts are set up? Whose approvals are required?

What is the Status of these of Trusts under Income Tax (i.e. AOP, BOI, or Trust etc.)??

Please kindly suggests.

Thanks.