The Symmetry Elements linked with a molecule are:-

Symmetry Elements

(i) A Proper Axis of Rotation: C_n where n = 1,.... 
This implies n-fold rotational symmetry about the axis.

(ii) A Plane of Reflection: s 
This implies bilateral symmetry concerning the plane. 
These planes are further confidential as:

s_h - Horizontal Plane which is perpendicular to the Principal Axis of Rotation (i.e. Axis with highest value of n). If no principal axis exists s_h is distinct as the molecular plane.

s_v or s_d - Vertical Plane which holds the Principal Axis of Rotation and is perpendicular to a s_h plane, if it exists. When mutually s_v and s_d planes are present, the s_v planes hold the superior number of atoms, the s_d planes enclose bond angle bisectors. If only one type of vertical plane is present, s_v or s_d may be used depending on the entirety symmetry of the molecule.

(iii) A Center of Inversion - i 
This is a central point throughout which all C_n and s elements have to pass. If no such ordinary point exists there is refusal center of symmetry.

(iv) Improper Axis: S_n 
This is invented of two parts: C_n and s_h both of which may or may not be factual symmetry elements of the molecule. If equally the C_n and s_h are there then S_n must also exist. The following relations are obliging in this stare: 
(a) If n is even, S_nⁿ = E 
(b) If n is odd, S_nⁿ = s and S_n²ⁿ = E 
(c) If m is even, S_n^m = C_n^m when m < n 
S_n^m = C_n^m-n when m > n 
(d) If S_n with even n exists then C_n/2 exists. 
(e) If S_n with odd n exists then both C_n and s perpendicular to C_n exist.