Is 2oh−+ca2+−> 2ca(oh)2 balanced

No.

Explanation:

No.  There is 1 atom of Ca on the left and 2 Ca's on the right  and 2 OH's on the left and 4 on the right.

The balanced equation is:

4OH-  +  2Ca2+ >  2Ca(OH)2.

Is not balanced

Explanation:

For an equation to be balanced there must be on each side of the equation the same amount of each atom.

2 OH−  +  Ca 2+   > 2 Ca(OH)2

On the left we have the following amounts of atoms:

Ca = 1

O = 2

H = 2

Total charges =  0

And on the right:

Ca = 2

O = 4

H = 4

Total charges =  0

We can see that on the right we have twice as many atoms as on the left, so we can delete a molecule of Ca(OH)2

                         2 OH−  +  Ca 2+   >  Ca(OH)2

Now the equation is balanced because there are the same number of atoms on both sides and also the charges are equal in both sides.