Charegable gains

Ques – Rodney died on 13 August 2020. In his will he left £200 in cash to each of his five nephews,
investments held in ISAs valued at £350,000 to his daughter, and the residue of his estate,
which amounted to £520,000, to his wife.
What is the chargeable estate for inheritance tax purposes?

As per my understanding here , its a transfer of main residence and therefore only 175k will be exempted, however as per answer they have fully exempt it ?

I am not sure why , please help!