$1.$ The classification of welding processes into $\_$ and $\_$ types is based on the nature of the electrode used and the source of heat or friction generated during the welding process. $($Options: consumable, non$-$consumable, fusion, solid state$)$

$2.$ In diffusion welding, the pressure applied to the workpieces is typically less than $\_$ MPa, requiring a clean and $\_$ surface for effective bonding without melting the base materials. $($Options: $5,10,15,$ flat, rough$)$