**Greatest 7-digit number**

The greatest 7-digit number is a number that has 7 digits and is the largest possible number that can be formed using those digits. In this case, we need to find the greatest 7-digit number using the digits 1, a, b, c, d, and e. Let's go through each option and determine the greatest number for each.

**(a) Ten Lakh**

Ten lakh refers to 10,00,000. To form the greatest 7-digit number using the digits given, we need to place the digits in descending order. Since we have the digits 1, a, b, c, d, and e, we can arrange them in descending order as follows: 9, 8, 7, 6, 5, 4, 3, 2, 1. Therefore, the greatest 7-digit number with ten lakh is 9876543.

**(b) One Crore**

One crore refers to 1,00,00,000. Similarly, we can arrange the digits in descending order to find the greatest 7-digit number with one crore. Using the digits 1, a, b, c, d, and e, we can arrange them as follows: 9, 8, 7, 6, 5, 4, 3, 2, 1. Therefore, the greatest 7-digit number with one crore is 9876543.

**(c) One Thousand**

One thousand refers to 1,000. Since we only have the digits 1, a, b, c, d, and e, we cannot form a 7-digit number with one thousand.

**(d) One Lakh**

One lakh refers to 1,00,000. Arranging the digits in descending order, we get: 9, 8, 7, 6, 5, 4, 3, 2, 1. Therefore, the greatest 7-digit number with one lakh is 9876543.

**(e) Ten Thousand**

Ten thousand refers to 10,000. Similarly, arranging the digits in descending order, we get: 9, 8, 7, 6, 5, 4, 3, 2, 1. Therefore, the greatest 7-digit number with ten thousand is 9876543.

Overall, the greatest 7-digit number using the given digits 1, a, b, c, d, and e is 9876543.

10,00,000 Ten lakh or one million