For an n$-$channel MOSFET $($p$-$type substrate$)$ with a Si $/$ SiO $2$ interface charge of Q ss $=1\mathrm{.}602$e$-9$ C$/$cm $2,$ what is the effect of decreasing the oxide thickness on the following; circle one for each and explain:

$($a$)$ The flat$-$band voltage. increase decrease no change not sure

$($b$)$ The threshold voltage increase decrease no change not sure