When the final velocity is less than the initial velocity, this is question 4 options: speed time acceleration deceleration

The correct choice is deceleration.

we know that

v = v₀ + at

v = final velocity  , v₀ = initial velocity , a = acceleration , t = time

In deceleration , net force acts in opposite direction of motion of the object. this net force produce acceleration is in opposite direction of motion of the object. hence the value of such acceleration is taken as positive if the velocities are in positive direction. this acceleration work to slow down the object instead of accelerating it. hence the final velocity of the object is smaller as compared to initial velocity.

colorless gas, exhibiting a blue glow when placed in an electric field

b) solid

its a type of rock