Hi Tanvi,

Make it required

[required]
public virtual IList<QuestionnaireAnswerBlock> Answers { get; set; }

And if you want to customize the validation message then create a custom validation attribute. The solution I mentioned in your other question

https://world.episerver.com/forum/developer-forum/-Episerver-75-CMS/Thread-Container/2020/6/how-to-limit-number-of-elements-in-ilist-with-only-minimum-elements-value/

As Ravindra suggested you can just use a required attribute.

Or, if you want to be able to valdiate a specific number of items, how about a validation attribute like this:

[AttributeUsage(AttributeTargets.Property)]
public class MinItemsAttribute : ValidationAttribute
{
	private readonly int _minAllowed;

	public MinItemsAttribute(int minAllowed)
	{
		_minAllowed = minAllowed;
	}

	protected override ValidationResult IsValid(object value, ValidationContext validationContext)
	{
		var linkItemCollection = value as LinkItemCollection;

		if (linkItemCollection != null && ValidateMinAllowed(linkItemCollection.Count))
		{
			return ValidationResult.Success;
		}

		var contentArea = value as ContentArea;

		if (contentArea?.Items != null && ValidateMinAllowed(contentArea.Count))
		{
			return ValidationResult.Success;
		}

		var enumerable = value as IEnumerable;

		if (enumerable != null && ValidateMinAllowed(enumerable.Cast<object>().Count()))
		{
			return ValidationResult.Success;
		}

		return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
	}

	private bool ValidateMinAllowed(int count)
	{
		return count >= _minAllowed;
	}

	public override string FormatErrorMessage(string name)
	{
		return !string.IsNullOrEmpty(ErrorMessage) ? ErrorMessage : $"{name} requires at least {_minAllowed} items.";
	}
}

It'll work on a Link Item Collection, Content Area or IList<>.

Using it is as simple as:

[MinItems(2)]
public virtual IList<QuestionnaireAnswerBlock> Answers { get; set; }

You can customize the error message as well:

[MinItems(2, ErrorMessage = "Please add at least 2 values to the list")]
public virtual IList<QuestionnaireAnswerBlock> Answers { get; set; }