The cyclohexane ring is essentially free of ring strain because check all that apply.
in cyclohexane, the c−c−c angle is very close to the tetrahedral angle.
all the carbon-hydrogen bonds are staggered.
the ring strain is independent of the number of ch2 groups.
bond angles are not optimal in the cyclohexane ring.
the carbon-hydrogen bonds in cyclohexane are always eclipsed.
there are no eclipsed bonds in cyclohexane.

The following statements are correct: 1,2 and 6

Explanation:

1.The cyclohexane ring adopts a chair conformation in order to minimize its torsional strain. In chair conformation 4 carbon atoms are in one plane 1 carbon atom is above that plane and the other 1 carbon atom is below that plane .This leads to  chair conformation in which the bond angles are very close to the ideal tetrahedral angle of 109.5 degrees. The C-C-C bond angle in chair conformation is 110 degrees which is almost equal to the ideal tetrahedral angle.

2. In cyclohexane molecule as the molecule adopts a chair conformation in order  to eliminate the torsional strain which would occur if the cyclohexane ring were to be planar. Torsional strain is basically the inter electronic repulsion between the atoms that do not share a bond. So this strain happens on account of eclipsing atoms. In case of eclipse structure there would be a lot of torsional strain. In case of chair conformation all the C-H bonds happen to be completely staggered in nature to eliminate the torsional strain.

3. The ring strain in case of cycloalkanes are  dependent upon the number of CH₂ groups present as that would determine the size of the ring and subsequently its structure ,whether the ring would be 5 , 6 or 7 membered  .Cyclohexane is a 6 -membered as there are 6CH₂ groups in it and the existence of chair conformation is only for Cyclohexane or for molecules having 6-membered ring  . Any change  in number of CH₂groups would lead to a different conformational structure.

4.All the bond angles in cyclohexane ring is  approximately 110 degrees which is almost equal to the ideal terahedral bond angle. So the bond angles in cyclohexane are optimal.

5.The C-H bonds in cyclohexane are  always staggered and never eclipsed in order to reduce there torsional strain.

6.All the bonds in cyclohexane ring are staggered to eliminate the torsional strain. It is quite evident that the cyclohexane ring is completely stable free of the ring strain.So there are no eclipsing bonds present in cyclohexane.

So the statements which are correct 1,2 and 6

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  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-