Answer:
The correct option is methane :
.
Explanation:
Average speed of the gas molecules id given by expression:

k = Boltzmann cosnatnt
T = Temperature of the gas molecules = 355 K
m = molecular mass of the molecule

Molar mass of methane = 18 g/mol
Molar mass of neon = 20.18 g/mol
Molar mass of ethene = 28 g/mol
Molar mass of chlorine gas = 70 g/mol
Lower the value of molar mass of gas molecule higher will be the average speed.So, from the given options methane gas greatest average seed because it has lowest molecular mass
The block’s average speed : 0.36 m/s
<h3>Further explanation</h3>
Distance is the length traveled by an object within a certain of time .
Average speed = total distance/total amount of time ,
Can be formulated :

ΔD= total distance
Δt= total time
A block is pulled 0.90 m to the right in 2.5 s :
ΔD= total distance = 0.9 m
Δt= total time = 2.5 s
The block’s average speed :

Ionization energy is the measure of the extend to which the nucleus attracts the outermost electron
if ionization energy us high than force of attraction Is high so it is not easy to remove and vice versa .
hope you understand.....