why is lead not affected by dilute hcl in cold???

Dear student,

We cannot say lead is not affected by dilute acids. Actually it is affected by them. When lead reacts with dilute acids,( Dil. HCl and Dil. sulphuric acid)
It forms insoluble lead(II)chloride and lead(II)sulphate which forms a coating over the lead and prevent further reaction. This reaction is spontaneous and it seems like lead remains unreacted. Actually, lead reacts to form respective compound and liberates hydrogen (H²) on reaction with acids.