Sharepoint - Assign Unique permission to SharePoint 2013 List using Client Side code C#

Ok I figured out, I used the below code:

public static void AddPermission(ClientContext cpx, List list,
                                 string groupName, string permissionName)
{
    //  Web web = cpx.Web;
    //  Site site = cpx.Site;
    var GRoup1 = cpx.Web.SiteGroups.GetByName(groupName);
    var roletypes= cpx.Web.RoleDefinitions.GetByType(RoleType.Contributor);
    cpx.ExecuteQuery();
    list.BreakRoleInheritance(true, false);
    RoleDefinitionBindingCollection collRoleDefinitionBinding = 
         new RoleDefinitionBindingCollection(cpx);
    collRoleDefinitionBinding.Add(roletypes);
    list.RoleAssignments.Add(GRoup1, collRoleDefinitionBinding);
    cpx.ExecuteQuery();
}