Dear sir,
Your question is above sum received on maturity of Life insurance policy is exempt or taxable. Before going into detail, let me clear the answer in with two points;-

1. Sum received on maturity of Life insurance policies which covered under 10(10D) is Exempt. 
2. Sum received on policies not covered under 10(10D) is Taxable. 

Now the point is which are the policies covered in section 10(10D) and what are the conditions of exemptions. First of all, check your policy documents, if your policy is covered under 10(10D) then it is clearly mentioned in your policy documents. If not mentioned then it is not covered. 
Now coming to conditions of section 10(10D);-
Exemption under section 10(10D) is available on any amount received under a life insurance policy including death benefits, maturity benefits and, accrued bonus. Further The entire amount received under a life insurance policy is exempt under section 10(10D). Meaning thereby that there is no upper limit applicable to the claim against the life insurance policy. There are certain exceptional cases, wherein, the this exemption is not available as given below:-
Exemption under section 10(10D) of the Income Tax Act is not available under the following circumstances-
1. Any sum received under section 80DD(3) of the Income Tax Act. Any sum received under section 80DDA(3) of the Income Tax Act.(Receipts under a policy for taken for maintenance of a dependent, being a person with disability)
2. Any amount received under the Keyman Insurance Policy.

Please note ‘Keyman Insurance Policy’ means the life insurance policy taken by a person-

• On the life of another person who is (or was) the employee of the first mentioned person; or
• On the life of another person who is (or was) connected, in any manner, with the business of the first mentioned person.

3. Any sum received under an insurance policy, if the following criteria are satisfied-

Sr. No.
Criteria of the period of issue of insurance policy
Criteria of premium

1
The insurance policy issued on or after 1st April 2003 but on or before 31st March 2012
The premium payable, exceeds 20% of the actual capital sum assured, for any of the years (during the term of the policy).

2
The insurance policy issued on or after 1st April 2012
The premium payable, exceeds 10% of the actual capital sum assured, for any of the years (during the term of the policy).

Further, it is also relevant to note here that in sr. no. 2 above (under criteria of premium) the premium payable, for any of the years, exceeds 15% (instead of 10%) of the actual capital sum assured would be applicable in case the following points are satisfied-
1. The insurance policy issued on or after 1st April 2013; and
2. The insurance policy is in respect of the life insurance of-

• The person with a disability or the person with severe disability (as referred under section 80U); or
• The person suffering from disease or ailment as referred in rules made under section 80DDB.

(Hence Any money received from a life insurance policy, where the premium is more than 10% or 20% (as per dates given above )of the sum assured as the case may be, is fully taxable.
It is important to note here that exemption under section 10(10D) is available against any amount received on the death of a person (even if the criteria mentioned, in the table above, at sr. no. 1 or sr. no. 2 is satisfied).
 
Coming to your case, you paid a single premium of Rs. 501801/- for a life insurance policy taken after 1-4-2012, your premium is more than 10% of the sum assured, hence sum received under this policy is not covered by section 10(10D) hence it is taxable.