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Gurmeet Singh posted an Question

October 01, 2020 • 22:57 pm

30 points

IIT JAM
Geology (GG)

Sir what is 'i' and how to solve this question

Question 29/60 If1S added to 4 2m, which crystal class is formed ? (A) 4mm (B) 422 4 2 2 (C) (D) No change m m View Solution 4 22 m m m

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Sajan sarthak

i" is the inversion center. Inversion center (i) is a type of symmetry element which creates an inverted face for all available faces. And if we add it with 4bar 2 m it will create 4/m 2/m 2/m and if any odd symbol like 3bar or 1 bar there is already a" i" symmetry in default
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sir, the central 2 , usko m/2 nhi krna chiye? and last wala 2 kaise aaya sir as there only m given. it should be 1/m?
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dear gurmeet you should always know the basic of HM symbol 4bar 2 m is a tetragonal system point group so last symbol indicates axes bisecting the a1& a2
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Rahul kumar Best Answer

"i" is the inversion center. Inversion center (i) is a type of symmetry element which creates an inverted face for all available faces. Addition of "i" in bar4 2 m point group will create an inverted face of all faces and hence it will result into a symmetry associated with point group 4/m 2/m 2/m. In simple words, bar4 2 m + i = 4/m 2/m 2/m
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sir we have only 42
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42 is not a point group. In question it is written as bar4 2 m; which means that one four fold rotoinversion axis, two fold axis and mirror plane
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