Is the lack of knowledge a form of sin?
i dont think lack of knowledge is sin by itself,
but every one can research, ponder and God helps him-her.
God says in the holy Quran verse 69 of chapter 29:
وَالَّذِينَ جَاهَدُوا فِينَا لَنَهْدِيَنَّهُمْ سُبُلَنَا وَإِنَّ اللَّهَ لَمَعَ الْمُحْسِنِينَ ﴿۶۹﴾
And (as for) those who strive hard for Us, We will most certainly guide them in Our ways; and Allah is most surely with the doers of good.
so, accessing knowledge, is striving path in the way of God, God helps us and rewards us.