Which sentence is correct?

With words that indicate portions—percent, fraction, part, majority, some, all, any, none, …and half:
—look at the noun in your of phrase (object of the preposition) to determine whether to use a singular or plural verb. If the object of the preposition is singular, use a singular verb. If the object of the preposition is plural, use a plural verb.

'group' is the object of the preposition, and is singular. Hence, use ' is '.