The opposite side would be 1... Opposite sides of a standard dice always add up to seven.
Opposite sides of a dice add up to 7
Opposite dice sides always total 7
The opposite sides of dice always add up to seven, therefore your answer is six
A standard cube die has 6. Other dice (as used by D&D players, etc) have 4 sides (tetrahedral dice), 8 sides (octahedral dice), 12 sides (dodecahedral dice) or 20 sides (icosahedral dice).
Yes. 1-6 3-4 and 2-5.
SIX sides
21
They add up to 7
It is 7
There is no actual 'necessity' for the opposite sides to add to seven. As long as the numbers are all present, the die would still be fair and proper, and the probability of rolling any particular number would be constant - 1/6. Custom and practice is the only reason that the numbers are arranged so that they add to seven. I suppose it prevents arguments - if a player was loosing at a dice game they might be tempted to claim that the dice are non-standard if they were different from other dice.
If the type of solid (die) is a Platonic solid, then the opposite sides add to the number of faces plus one. For example, a cube's opposite sides add to seven.