What is the largest value in the sequence generated by the formula an = –n2 + 6n – 7?
a. 1
b. 2
c. 3
d. 4

Derive the equation and equate the derivative to zero.
                              dan/dt = -2n + 6 = 0
The value of n in the equation is 3. We substitute 3 to the original equation,
                                           an = -(3)² + 6(3) - 7 = 2
The answer to this item is letter B. 

Element 17 is chlorine it is a group 7 element(halogen) and belongs to period 3 of the periodic table

Where is the qeustion