Yes, science background is very much necessary for NATA. B. Arch is a course which falls under engineering. You need both physics chemistry and maths to be an architect. But dont worry NATA's question paper will cover only the 11-12th science syllabus which you will already know if you belong from science background. 

NATA SYLLABUS

NATA measures drawing and observation skills, sense of proportion, aesthetic sensitivity and critical thinking ability by 2parted exams.
first part- paper based drawing test
second part- online test with MCQs on Physics, Chemistry, Mathematics and General Aptitude Test. 

1.Drawing includes memory drawing, shades, shadows, 2D compositions, visualisation, perspective drawing etc. NATA drawing part is totally depend on your creativity and ability. You need to practice more and more to improve your skills and ideas. You need to be creative, because creativity is necessary in this field. 

2. Aptitude test includes Diagrammatic Reasoning, Numerical Reasoning, Verbal Reasoning, Inductive Reasoning, Situational Judgment, Logical Reasoning, Abstract Reasoning. 

3. Mathematics include algebra, logarithm, matrices, trigonometry, coordinate geometry, 3D coordination of geometry, theory of calculus, application of calculus, permutation and combination, statistics and probability.

4. NATA also includes questions from Physics and chemistry in which class 10-12 studies are important. As well as includes general aptitude test with mathematical reasoning, sets and relations. 

Eligibility criteria-

NATA Eligibility Criteria is divided into 4 sections such as age, qualification, subject, minimum marks. The candidates must be eligible for all the 4 sections in order to qualify NATA. 

• Age- Fortunately, there is no age limit now to qualify NATA. 
• Qualification- Qualifying 10+2 examination in with the subjects Physics Chemistry maths from any recognized board is must for the candidates. Or candidates who have qualified 10+3 with mathematics from any recognized board can also eligible for NATA. 
• Subject- The candidates must have Physics, chemistry and mathematics as a mandatory subjects to be eligible for NATA. candidates from arts stream can be eligible too only if they are qualified the physics, chemistry and mathematics exams conducted by CBSC
• Marks- The candidates must score minimum of 50% marks in their qualifying examination and 50% marks in Physics, chemistry and maths. 5% relaxation has been given to SC, ST, OBC-NCL category or PwD candidates.

Hope this helps! 

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know how to apply for NATA

https://designfresher.com/forum/question/how-can-i-apply-for-nata