My son has secured 423 in NEET EXAM. in general merit no other quata is applicable to us.So is there in any chances of getting govt. colleg

With 423 makes and without any quota,  government medical college looks almost impossible to be straight forward to you ma'am. But yes he can try for Private medical colleges if the fees are affordable to you. Or changing the courses and going for BDS, BHMS or BAMS is also another option. All depends on you. He can also go for BSc is he wants to OR even taking a drop and repeating the exam for MBBS medical govt clg isn't a bad option either as well. But he has to give his best this year for sure. The decision is with you.

Best wishes.