SELECT * FROM question_mgmt as q WHERE id=1291 AND status=1 SELECT id,question_no,question,chapter FROM question_mgmt as q WHERE courseId=2 AND subId=9 AND chapterId=43 and ex_no='1' AND status=1 ORDER BY CAST(question_no AS UNSIGNED)

Question:

An element with mass number 81 contains 31.7% more neutrons as compared to protons. Assign the atomic symbol.

Answer:

Mass number = 81 i.e p + n = 81

Let us suppose number of protons = x and neutrons

= x+31.7Xx /100 = 1.317x

Therefore x + 1.317x = 81

Or

2.317x = 81

Or x = 81/2.317 = 35 T

hus number of protons = 35 ,i.e atomic number = 35

Hence the symbol is 8135 Br


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