"The committee has been given a wide-ranging" should be corrected to "a wide-ranging mandate," as "wide-ranging" is a compound adjective that should be hyphenated.
"Mandate that included examining the feasibility" is grammatically correct.
"Of a national law to ban cow" is correct.
"Slaughter by amending the constitution" is grammatically correct, but "Constitution" should be capitalized as it refers to the national document.
Therefore, the error is in option (1), where "wide ranging" should be corrected to "wide-ranging."