Losing 1-0 to Porto in the first leg was really unfortunate for Arsenal as they played quite overwhelmingly but did not score a goal. Porto is always an unpleasant opponent in the UCL, but looking back at the teams entering the qualifying round, this is a much easier opponent for them. Hopefully the Emirates home field will help Arsenal play more confidently and win against Porto in the second leg.
The first leg was really painful for Arsenal who came quite spectacularly after previously winning in the league with a big score but they had to lose at home to Porto without even having a single shot at the opponent goal, Arsenal game in the first leg was actually quite good and was even able to continue to dominate the game throughout match, but the tight defense built by Porto meant that all attacks carried out by Arsenal were able to be overcome by Porto defense outside the penalty box, the defeat against Porto was actually a warning for Arsenal because they currently need a striker who is capable of being the difference between if Arsenal wing attackers experienced a deadlock.
The second leg will be a match that can be said to be life and death for Arsenal in the Champions League, because if they lose or even draw then it is certain that the Champions League will end too quickly for Arsenal, but Porto cannot underestimate Arsenal at home because after all Arsenal is a team that is quite dangerous when playing in front of its own supporters, I think in the second leg the Arsenal players will play all out to at least be able to catch up on the goals left behind and maybe even a big win will be achieved by Arteta team later in emirates stadium.
In fact, these two clubs have almost similar performance if we both pay attention to the performance of both clubs and both clubs will both be superior when competing at their respective home grounds, such as Porto can win in the 1st leg and of course in the 2nd leg Arsenal far superior.
Bookies will still favor Arsenal in this match because we can also see that in the 1st leg Arsenal did not concede more than 1 score and that means Arsenal has great strength to be stronger at home.
Unless something happens that is unexpected, such as Arsenal's main striker or Arsenal's main defender getting injured because we don't know what will happen because there are still 2 weeks remaining and in the remaining time a lot can happen but I hope Arsenal will be fine and can proceed to the next round.