Assalamu Olaikum. 1.During offering Salah after Imam in a Zamat,if a muttaqin/follower makes any mistakes (reciting Tasbeeh,Darood other things in wrong accent etc.),would his prayer consider to be valid, what is your opinion according Quran & Hadith. 2.Recently, an young office colleague died at the age of 33, how we pray for him ? Allah hafez

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If one makes a mistake in the prayer, then we have to look at the kind of the mistake he made, because the mistake may or may not invalidate his prayer. What you mentioned in the question was that the person led in prayer made a mistake in pronouncing the Tasbeeh or in exalting the mention of the Prophet . The answer is that if the mistake is in the Tasbeeh when in the position of bowing or when prostrating or a mistake in exalting the mention of the Prophet then being led by an Imaam makes up for such a mistake and he does not have to prostrate for forgetfulness because he made such a mistake while being led by an Imaam. Ibn Qudaamah said: “If a person led in prayer forgets while the person leading him did not forget, then he does not have to prostrate for forgetfulness according to the view of the majority of the scholars .”

As regards your second question, which is supplicating for the dead in the funeral prayer, then there are many versions for this. For instance, the Prophet led a funeral prayer and supplicated: “O Allaah! Forgive him, have mercy upon him, give him peace and absolve him. Receive him with honour and make his grave spacious; wash him with water, snow and hail. Cleanse him from faults as a white garment is cleansed from impurity. Requite him with an abode more excellent than his abode, with a family better than his family, and with a spouse better than his spouse. Admit him to Paradise, and protect him from the torment of the grave and the torment of Hellfire.” [Muslim].

It is also confirmed that when the Prophet would lead a funeral prayer, he would supplicate: ''O Allaah, forgive our living and our dead, those present and those absent, our young and our old, our males and our females.  O Allaah, whom amongst us You keep alive, then let him live upon Islam, and whom amongst us You take unto Yourself, then let such a death be upon faith.'' [Abu Daawood].

You may also supplicate with the following Prophetic supplication: “O Allaah, he is Your slave and the son of Your maid-slave and the son of Your Slave, he used to bear witness that None has the right to be worshipped but Allaah and that Muhammad is Your Slave and Messenger and you are all knowledgeable of his situation. If he was righteous then increase his reward and if he was wicked then overlook his sins. O Allaah, do not deprive us of his reward and do not let us stray after him.'' [Maalik].

The above are some narrations from the Prophet and whoever memorizes such supplications and supplicates with them, then this is good, and whoever does not memorize them, he may supplicate for the deceased with any supplication whether during the prayer or outside the prayer, like supplicating: “O Allaah! Have mercy upon him, and overlook his sins, O Allaah, reward him for his good deeds with a good reward, and forgive his sins and have mercy upon him.”; and one may supplicate with any other supplications.  

Allaah Knows best.