Hi can someone pls help me with number 9

Significant figures are digits read directly from the measuring instrument plus one more digit, which is __ by the observer.

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.

Voltaic cells produce a positive overall charge. what does this indicate? a. the reaction is likely to be endothermic. b. the reaction is spontaneous. c. the reaction is not likely to occur. d. the reaction is not spontaneous.